Methods for signaling video coding data

ABSTRACT

The present disclosure provides systems and methods for wrap-around motion compensation. One exemplary method comprises: receiving a wrap-around motion compensation flag; determining whether a wrap-around motion compensation is enabled based on the wrap-around motion compensation flag; in response to a determination that the wrap-around motion compensation is enabled, receiving data indicating a difference between a width of the picture and an offset used for determining a horizontal wrap-around position; and performing a motion compensation according to the wrap-around motion compensation flag and the difference.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority to and the benefits of priorityto U.S. Provisional Patent Application No. 63/000,443, filed on Mar. 26,2020. The provisional application is incorporated herein by reference inits entirety.

TECHNICAL FIELD

The present disclosure generally relates to video data processing, andmore particularly, to methods and apparatuses for signaling informationregarding wrap-around motion compensation, slice layout, and sliceaddress.

BACKGROUND

A video is a set of static pictures (or “frames”) capturing the visualinformation. To reduce the storage memory and the transmissionbandwidth, a video can be compressed before storage or transmission anddecompressed before display. The compression process is usually referredto as encoding and the decompression process is usually referred to asdecoding. There are various video coding formats which use standardizedvideo coding technologies, most commonly based on prediction, transform,quantization, entropy coding and in-loop filtering. The video codingstandards, such as the High Efficiency Video Coding (e.g., HEVC/H.265)standard, the Versatile Video Coding (e.g., VVC/H.266) standard, and AVSstandards, specifying the specific video coding formats, are developedby standardization organizations. With more and more advanced videocoding technologies being adopted in the video standards, the codingefficiency of the new video coding standards get higher and higher.

SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure provide a method for signalingvideo coding data, the method comprises: receiving a wrap-around motioncompensation flag; determining whether a wrap-around motion compensationis enabled based on the wrap-around motion compensation flag; inresponse to a determination that the wrap-around motion compensation isenabled, receiving data indicating a difference between a width of thepicture and an offset used for determining a horizontal wrap-aroundposition; and performing a motion compensation according to thewrap-around motion compensation flag and the difference.

Embodiments of the present disclosure further provide a method forsignaling video coding data, the method comprises: receiving a picturefor coding, wherein the picture comprises one or more slices; andsignaling, in a picture parameter set of the picture, a variableindicating a number of slices in the video frame minus 2.

Embodiments of the present disclosure further provide a method forsignaling video coding data, the method comprises: receiving a picturefor coding, wherein the picture comprises one or more slices and one ormore subpictures; and signaling, in a picture parameter set of thepicture, a variable indicating a number of slices in the picture minus anumber of subpictures in the picture minus 1.

Embodiments of the present disclosure further provide a method forsignaling video coding data, the method comprises: receiving a picturefor coding, wherein the picture comprises one or more slices; signalinga variable indicating whether a picture header syntax structure for thepicture is present within a slice header for the one or more slices; andsignaling a slice address according to the variable.

Embodiments of the present disclosure further provide a system forperforming video data processing, the system comprising: a memorystoring a set of instructions; and a processor configured to execute theset of instructions to cause the system to perform: receiving awrap-around motion compensation flag; determining whether a wrap-aroundmotion compensation is enabled based on the wrap-around motioncompensation flag; in response to a determination that the wrap-aroundmotion compensation is enabled, receiving data indicating a differencebetween a width of the picture and an offset used for determining ahorizontal wrap-around position; and performing a motion compensationaccording to the wrap-around motion compensation flag and thedifference.

Embodiments of the present disclosure further provide a system forperforming video data processing, the system comprising: a memorystoring a set of instructions; and a processor configured to execute theset of instructions to cause the system to perform: receiving a picturefor coding, wherein the picture comprises one or more slices; andsignaling, in a picture parameter set of the picture, a variableindicating a number of slices in the video frame minus 2.

Embodiments of the present disclosure further provide a system forperforming video data processing, the system comprising: a memorystoring a set of instructions; and a processor configured to execute theset of instructions to cause the system to perform: receiving a picturefor coding, wherein the picture comprises one or more slices and one ormore subpictures; and signaling, in a picture parameter set of thepicture, a variable indicating a number of slices in the picture minus anumber of subpictures in the picture minus 1.

Embodiments of the present disclosure further provide a system forperforming video data processing, the system comprising: a memorystoring a set of instructions; and a processor configured to execute theset of instructions to cause the system to perform: receiving a picturefor coding, wherein the picture comprises one or more slices; signalinga variable indicating whether a picture header syntax structure for thepicture is present within a slice header for the one or more slices; andsignaling a slice address according to the variable.

Embodiments of the present disclosure further provide non-transitorycomputer readable medium that stores a set of instructions that isexecutable by one or more processors of an apparatus to cause theapparatus to initiate a method for performing video data processing, themethod comprising: receiving a wrap-around motion compensation flag;determining whether a wrap-around motion compensation is enabled basedon the wrap-around motion compensation flag; in response to adetermination that the wrap-around motion compensation is enabled,receiving data indicating a difference between a width of the pictureand an offset used for determining a horizontal wrap-around position;and performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

Embodiments of the present disclosure further provide non-transitorycomputer readable medium that stores a set of instructions that isexecutable by one or more processors of an apparatus to cause theapparatus to initiate a method for performing video data processing, themethod comprising: receiving a picture for coding, wherein the picturecomprises one or more slices; and signaling, in a picture parameter setof the picture, a variable indicating a number of slices in the videoframe minus 2.

Embodiments of the present disclosure further provide non-transitorycomputer readable medium that stores a set of instructions that isexecutable by one or more processors of an apparatus to cause theapparatus to initiate a method for performing video data processing, themethod comprising: receiving a picture for coding, wherein the picturecomprises one or more slices and one or more subpictures; and signaling,in a picture parameter set of the picture, a variable indicating anumber of slices in the picture minus a number of subpictures in thepicture minus 1.

Embodiments of the present disclosure further provide non-transitorycomputer readable medium that stores a set of instructions that isexecutable by one or more processors of an apparatus to cause theapparatus to initiate a method for performing video data processing, themethod comprising: receiving a picture for coding, wherein the picturecomprises one or more slices; signaling a variable indicating whether apicture header syntax structure for the picture is present within aslice header for the one or more slices; and signaling a slice addressaccording to the variable.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and various aspects of the present disclosure areillustrated in the following detailed description and the accompanyingfigures. Various features shown in the figures are not drawn to scale.

FIG. 1 shows structures of an example video sequence, according to someembodiments of the present disclosure.

FIG. 2A shows a schematic of an example encoding process, according tosome embodiments of the present disclosure.

FIG. 2B shows a schematic of another example encoding process, accordingto some embodiments of the present disclosure.

FIG. 3A shows a schematic of an example decoding process, according tosome embodiments of the present disclosure.

FIG. 3B shows a schematic of another example decoding process, accordingto some embodiments of the present disclosure.

FIG. 4 shows a block diagram of an example apparatus for encoding ordecoding a video, according to some embodiments of the presentdisclosure.

FIG. 5A shows a schematic of an example blending operation forgenerating reconstructed equirectangular projections, according to someembodiments of the present disclosure.

FIG. 5B shows schematic of an example cropping operation for generatingreconstructed equirectangular projections, according to some embodimentsof the present disclosure.

FIG. 6A shows a schematic of an example horizontal wrap-around motioncompensation process for equirectangular projections, according to someembodiments of the present disclosure.

FIG. 6B shows a schematic of an example horizontal wrap-around motioncompensation process for padded equirectangular projections, accordingto some embodiments of the present disclosure.

FIG. 7 shows syntax of an example high level wrap-around offset,according to some embodiments of the present disclosure.

FIG. 8 shows semantics of an example high level wrap-around offset,according to some embodiments of the present disclosure.

FIG. 9 shows a schematic of an example slice and subpicture partitioningof a picture, according to some embodiments of the present disclosure.

FIG. 10 shows a schematic of an example slice and subpicturepartitioning of a picture having different slices and subpictures,according to some embodiments of the present disclosure.

FIG. 11 shows syntax of an example picture parameter set for tilemapping and slice layouts, according to some embodiments of the presentdisclosure.

FIG. 12 shows semantics of an example picture parameter set for tilemapping and slice layouts, according to some embodiments of the presentdisclosure.

FIG. 13 shows syntax of an example slice header, according to someembodiments of the present disclosure.

FIG. 14 shows semantics of an example slice header, according to someembodiments of the present disclosure.

FIG. 15 shows syntax of an example improved picture parameter set,according to some embodiments of the present disclosure.

FIG. 16 shows semantics of an example improved picture parameter set,according to some embodiments of the present disclosure.

FIG. 17 shows syntax of an example picture parameter set with a variablewraparound_offset_type, according to some embodiments of the presentdisclosure.

FIG. 18 shows semantics of an example improved picture parameter setwith a variable wraparound_offset_type, according to some embodiments ofthe present disclosure.

FIG. 19 shows syntax of an example picture parameter set with a variablenum_slices_in_pic_minus2, according to some embodiments of the presentdisclosure.

FIG. 20 shows semantics of an example improved picture parameter setwith a variable num_slices_in_pic_minus2, according to some embodimentsof the present disclosure.

FIG. 21 shows syntax of an example picture parameter set with a variablenum_slices_in_pic_minus_subpic_num_minus1, according to some embodimentsof the present disclosure.

FIG. 22 shows semantics of an example improved picture parameter setwith a variable num_slices_in_pic_minus_subpic_num_minus1, according tosome embodiments of the present disclosure.

FIG. 23 shows syntax of an example updated slice header, according tosome embodiments of the present disclosure.

FIG. 24 shows a flowchart of an example video coding method with avariable signaling a difference between a width of a video frame and anoffset used for computing a horizontal wrap-around position, accordingto some embodiments of the present disclosure.

FIG. 25 shows a flowchart of an example video coding method with avariable signaling a number of slices in a video frame minus 2,according to some embodiments of the present disclosure.

FIG. 26 shows a flowchart of an example video coding method with avariable signaling a variable indicating a number of slices in the videoframe minus a number of subpictures in the video frame minus 1,according to some embodiments of the present disclosure.

FIG. 27 shows a flowchart of an example video coding method with avariable indicating whether a picture header syntax structure is presentwithin a slice header of a video frame, according to some embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments do not represent allimplementations consistent with the invention. Instead, they are merelyexamples of apparatuses and methods consistent with aspects related tothe invention as recited in the appended claims. Particular aspects ofthe present disclosure are described in greater detail below. The termsand definitions provided herein control, if in conflict with termsand/or definitions incorporated by reference.

The Joint Video Experts Team (JVET) of the ITU-T Video Coding ExpertGroup (ITU-T VCEG) and the ISO/IEC Moving Picture Expert Group (ISO/IECMPEG) is currently developing the Versatile Video Coding (VVC/H.266)standard. The VVC standard is aimed at doubling the compressionefficiency of its predecessor, the High Efficiency Video Coding(HEVC/H.265) standard. In other words, VVC's goal is to achieve the samesubjective quality as HEVC/H.265 using half the bandwidth.

In order to achieve the same subjective quality as HEVC/H.265 using halfthe bandwidth, the Joint Video Experts Team (“JVET”) has been developingtechnologies beyond HEVC using the joint exploration model (“JEM”)reference software. As coding technologies were incorporated into theJEM, the JEM achieved substantially higher coding performance than HEVC.The VCEG and MPEG have also formally started the development of a nextgeneration video compression standard beyond HEVC.

The VVC standard has been developed recently and continues to includemore coding technologies that provide better compression performance.VVC is based on the same hybrid video coding system that has been usedin modern video compression standards such as HEVC, H.264/AVC, MPEG2,H.263, etc.

A video is a set of static pictures (or frames) arranged in a temporalsequence to store visual information. A video capture device (e.g., acamera) can be used to capture and store those pictures in a temporalsequence, and a video playback device (e.g., a television, a computer, asmartphone, a tablet computer, a video player, or any end-user terminalwith a function of display) can be used to display such pictures in thetemporal sequence. Also, in some applications, a video capturing devicecan transmit the captured video to the video playback device (e.g., acomputer with a monitor) in real-time, such as for surveillance,conferencing, or live broadcasting.

To reduce the storage space and the transmission bandwidth needed bysuch applications, the video can be compressed. For example, the videocan be compressed before storage and transmission and decompressedbefore the display. The compression and decompression can be implementedby software executed by a processor (e.g., a processor of a genericcomputer) or specialized hardware. The module or circuitry forcompression is generally referred to as an “encoder,” and the module orcircuitry for decompression is generally referred to as a “decoder.” Theencoder and the decoder can be collectively referred to as a “codec.”The encoder and the decoder can be implemented as any of a variety ofsuitable hardware, software, or a combination thereof. For example, thehardware implementation of the encoder and the decoder can includecircuitry, such as one or more microprocessors, digital signalprocessors (“DSPs”), application-specific integrated circuits (“ASICs”),field-programmable gate arrays (“FPGAs”), discrete logic, or anycombinations thereof. The software implementation of the encoder and thedecoder can include program codes, computer-executable instructions,firmware, or any suitable computer-implemented algorithm or processfixed in a computer-readable medium. Video compression and decompressioncan be implemented by various algorithms or standards, such as MPEG-1,MPEG-2, MPEG-4, H.26x series, or the like. In some applications, thecodec can decompress the video from a first coding standard andre-compress the decompressed video using a second coding standard, inwhich case the codec can be referred to as a “transcoder.”

The video encoding process can identify and keep useful information thatcan be used to reconstruct a picture. If information that wasdisregarded in the video encoding process cannot be fully reconstructed,the encoding process can be referred to as “lossy.” Otherwise, it can bereferred to as “lossless.” Most encoding processes are lossy, which is atradeoff to reduce the needed storage space and the transmissionbandwidth.

In many cases, the useful information of a picture being encoded(referred to as a “current picture”) can include changes with respect toa reference picture (e.g., a picture previously encoded orreconstructed). Such changes can include position changes, luminositychanges, or color changes of the pixels. Position changes of a group ofpixels that represent an object can reflect the motion of the objectbetween the reference picture and the current picture.

A picture coded without referencing another picture (i.e., it is its ownreference picture) is referred to as an “I-picture.” A picture isreferred to as a “P-picture” if some or all blocks (e.g., blocks thatgenerally refer to portions of the video picture) in the picture arepredicted using intra prediction or inter prediction with one referencepicture (e.g., uni-prediction). A picture is referred to as a“B-picture” if at least one block in it is predicted with two referencepictures (e.g., bi-prediction).

FIG. 1 shows structures of an example video sequence, according to someembodiments of the present disclosure. As shown in FIG. 1, videosequence 100 can be a live video or a video having been captured andarchived. Video 100 can be a real-life video, a computer-generated video(e.g., computer game video), or a combination thereof (e.g., a real-lifevideo with augmented-reality effects). Video sequence 100 can beinputted from a video capture device (e.g., a camera), a video archive(e.g., a video file stored in a storage device) containing previouslycaptured video, or a video feed interface (e.g., a video broadcasttransceiver) to receive video from a video content provider.

As shown in FIG. 1, video sequence 100 can include a series of picturesarranged temporally along a timeline, including pictures 102, 104, 106,and 108. Pictures 102-106 are continuous, and there are more picturesbetween pictures 106 and 108. In FIG. 1, picture 102 is an I-picture,the reference picture of which is picture 102 itself. Picture 104 is aP-picture, the reference picture of which is picture 102, as indicatedby the arrow. Picture 106 is a B-picture, the reference pictures ofwhich are pictures 104 and 108, as indicated by the arrows. In someembodiments, the reference picture of a picture (e.g., picture 104) canbe not immediately preceding or following the picture. For example, thereference picture of picture 104 can be a picture preceding picture 102.It should be noted that the reference pictures of pictures 102-106 areonly examples, and the present disclosure does not limit embodiments ofthe reference pictures as the examples shown in FIG. 1.

Typically, video codecs do not encode or decode an entire picture at onetime due to the computing complexity of such tasks. Rather, they cansplit the picture into basic segments, and encode or decode the picturesegment by segment. Such basic segments are referred to as basicprocessing units (“BPUs”) in the present disclosure. For example,structure 110 in FIG. 1 shows an example structure of a picture of videosequence 100 (e.g., any of pictures 102-108). In structure 110, apicture is divided into 4×4 basic processing units, the boundaries ofwhich are shown as dash lines. In some embodiments, the basic processingunits can be referred to as “macroblocks” in some video coding standards(e.g., MPEG family, H.261, H.263, or H.264/AVC), or as “coding treeunits” (“CTUs”) in some other video coding standards (e.g., H.265/HEVCor H.266/VVC). The basic processing units can have variable sizes in apicture, such as 128×128, 64×64, 32×32, 16×16, 4×8, 16×32, or anyarbitrary shape and size of pixels. The sizes and shapes of the basicprocessing units can be selected for a picture based on the balance ofcoding efficiency and levels of details to be kept in the basicprocessing unit.

The basic processing units can be logical units, which can include agroup of different types of video data stored in a computer memory(e.g., in a video frame buffer). For example, a basic processing unit ofa color picture can include a luma component (Y) representing achromaticbrightness information, one or more chroma components (e.g., Cb and Cr)representing color information, and associated syntax elements, in whichthe luma and chroma components can have the same size of the basicprocessing unit. The luma and chroma components can be referred to as“coding tree blocks” (“CTBs”) in some video coding standards (e.g.,H.265/HEVC or H.266/VVC). Any operation performed to a basic processingunit can be repeatedly performed to each of its luma and chromacomponents.

Video coding has multiple stages of operations, examples of which areshown in FIGS. 2A-2B and FIGS. 3A-3B. For each stage, the size of thebasic processing units can still be too large for processing, and thuscan be further divided into segments referred to as “basic processingsub-units” in the present disclosure. In some embodiments, the basicprocessing sub-units can be referred to as “blocks” in some video codingstandards (e.g., MPEG family, H.261, H.263, or H.264/AVC), or as “codingunits” (“CUs”) in some other video coding standards (e.g., H.265/HEVC orH.266/VVC). A basic processing sub-unit can have the same or smallersize than the basic processing unit. Similar to the basic processingunits, basic processing sub-units are also logical units, which caninclude a group of different types of video data (e.g., Y, Cb, Cr, andassociated syntax elements) stored in a computer memory (e.g., in avideo frame buffer). Any operation performed to a basic processingsub-unit can be repeatedly performed to each of its luma and chromacomponents. It should be noted that such division can be performed tofurther levels depending on processing needs. It should also be notedthat different stages can divide the basic processing units usingdifferent schemes.

For example, at a mode decision stage (an example of which is shown inFIG. 2B), the encoder can decide what prediction mode (e.g.,intra-picture prediction or inter-picture prediction) to use for a basicprocessing unit, which can be too large to make such a decision. Theencoder can split the basic processing unit into multiple basicprocessing sub-units (e.g., CUs as in H.265/HEVC or H.266/VVC), anddecide a prediction type for each individual basic processing sub-unit.

For another example, at a prediction stage (an example of which is shownin FIGS. 2A-2B), the encoder can perform prediction operation at thelevel of basic processing sub-units (e.g., CUs). However, in some cases,a basic processing sub-unit can still be too large to process. Theencoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “prediction blocks” or “PBs” inH.265/HEVC or H.266/VVC), at the level of which the prediction operationcan be performed.

For another example, at a transform stage (an example of which is shownin FIGS. 2A-2B), the encoder can perform a transform operation forresidual basic processing sub-units (e.g., CUs). However, in some cases,a basic processing sub-unit can still be too large to process. Theencoder can further split the basic processing sub-unit into smallersegments (e.g., referred to as “transform blocks” or “TBs” in H.265/HEVCor H.266/VVC), at the level of which the transform operation can beperformed. It should be noted that the division schemes of the samebasic processing sub-unit can be different at the prediction stage andthe transform stage. For example, in H.265/HEVC or H.266/VVC, theprediction blocks and transform blocks of the same CU can have differentsizes and numbers.

In structure 110 of FIG. 1, basic processing unit 112 is further dividedinto 3×3 basic processing sub-units, the boundaries of which are shownas dotted lines. Different basic processing units of the same picturecan be divided into basic processing sub-units in different schemes.

In some implementations, to provide the capability of parallelprocessing and error resilience to video encoding and decoding, apicture can be divided into regions for processing, such that, for aregion of the picture, the encoding or decoding process can depend on noinformation from any other region of the picture. In other words, eachregion of the picture can be processed independently. By doing so, thecodec can process different regions of a picture in parallel, thusincreasing the coding efficiency. Also, when data of a region iscorrupted in the processing or lost in network transmission, the codeccan correctly encode or decode other regions of the same picture withoutreliance on the corrupted or lost data, thus providing the capability oferror resilience. In some video coding standards, a picture can bedivided into different types of regions. For example, H.265/HEVC andH.266/VVC provide two types of regions: “slices” and “tiles.” It shouldalso be noted that different pictures of video sequence 100 can havedifferent partition schemes for dividing a picture into regions.

For example, in FIG. 1, structure 110 is divided into three regions 114,116, and 118, the boundaries of which are shown as solid lines insidestructure 110. Region 114 includes four basic processing units. Each ofregions 116 and 118 includes six basic processing units. It should benoted that the basic processing units, basic processing sub-units, andregions of structure 110 in FIG. 1 are only examples, and the presentdisclosure does not limit embodiments thereof.

FIG. 2A shows a schematic of an example encoding process, according tosome embodiments of the present disclosure. For example, encodingprocess 200A shown in FIG. 2A can be performed by an encoder. As shownin FIG. 2A, the encoder can encode video sequence 202 into videobitstream 228 according to process 200A. Similar to video sequence 100in FIG. 1, video sequence 202 can include a set of pictures (referred toas “original pictures”) arranged in a temporal order. Similar tostructure 110 in FIG. 1, each original picture of video sequence 202 canbe divided by the encoder into basic processing units, basic processingsub-units, or regions for processing. In some embodiments, the encodercan perform process 200A at the level of basic processing units for eachoriginal picture of video sequence 202. For example, the encoder canperform process 200A in an iterative manner, in which the encoder canencode a basic processing unit in one iteration of process 200A. In someembodiments, the encoder can perform process 200A in parallel forregions (e.g., regions 114-118) of each original picture of videosequence 202.

In FIG. 2A, the encoder can feed a basic processing unit (referred to asan “original BPU”) of an original picture of video sequence 202 toprediction stage 204 to generate prediction data 206 and predicted BPU208. The encoder can subtract predicted BPU 208 from the original BPU togenerate residual BPU 210. The encoder can feed residual BPU 210 totransform stage 212 and quantization stage 214 to generate quantizedtransform coefficients 216. The encoder can feed prediction data 206 andquantized transform coefficients 216 to binary coding stage 226 togenerate video bitstream 228. Components 202, 204, 206, 208, 210, 212,214, 216, 226, and 228 can be referred to as a “forward path.” Duringprocess 200A, after quantization stage 214, the encoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The encoder can add reconstructed residual BPU 222 to predicted BPU208 to generate prediction reference 224, which is used in predictionstage 204 for the next iteration of process 200A. Components 218, 220,222, and 224 of process 200A can be referred to as a “reconstructionpath.” The reconstruction path can be used to ensure that both theencoder and the decoder use the same reference data for prediction.

The encoder can perform process 200A iteratively to encode each originalBPU of the original picture (in the forward path) and generate predictedreference 224 for encoding the next original BPU of the original picture(in the reconstruction path). After encoding all original BPUs of theoriginal picture, the encoder can proceed to encode the next picture invideo sequence 202.

Referring to process 200A, the encoder can receive video sequence 202generated by a video capturing device (e.g., a camera). The term“receive” used herein can refer to receiving, inputting, acquiring,retrieving, obtaining, reading, accessing, or any action in any mannerfor inputting data.

At prediction stage 204, at a current iteration, the encoder can receivean original BPU and prediction reference 224, and perform a predictionoperation to generate prediction data 206 and predicted BPU 208.Prediction reference 224 can be generated from the reconstruction pathof the previous iteration of process 200A. The purpose of predictionstage 204 is to reduce information redundancy by extracting predictiondata 206 that can be used to reconstruct the original BPU as predictedBPU 208 from prediction data 206 and prediction reference 224.

Ideally, predicted BPU 208 can be identical to the original BPU.However, due to non-ideal prediction and reconstruction operations,predicted BPU 208 is generally slightly different from the original BPU.For recording such differences, after generating predicted BPU 208, theencoder can subtract it from the original BPU to generate residual BPU210. For example, the encoder can subtract values (e.g., greyscalevalues or RGB values) of pixels of predicted BPU 208 from values ofcorresponding pixels of the original BPU. Each pixel of residual BPU 210can have a residual value as a result of such subtraction between thecorresponding pixels of the original BPU and predicted BPU 208. Comparedwith the original BPU, prediction data 206 and residual BPU 210 can havefewer bits, but they can be used to reconstruct the original BPU withoutsignificant quality deterioration. Thus, the original BPU is compressed.

To further compress residual BPU 210, at transform stage 212, theencoder can reduce spatial redundancy of residual BPU 210 by decomposingit into a set of two-dimensional “base patterns,” each base patternbeing associated with a “transform coefficient.” The base patterns canhave the same size (e.g., the size of residual BPU 210). Each basepattern can represent a variation frequency (e.g., frequency ofbrightness variation) component of residual BPU 210. None of the basepatterns can be reproduced from any combinations (e.g., linearcombinations) of any other base patterns. In other words, thedecomposition can decompose variations of residual BPU 210 into afrequency domain. Such a decomposition is analogous to a discreteFourier transform of a function, in which the base patterns areanalogous to the base functions (e.g., trigonometry functions) of thediscrete Fourier transform, and the transform coefficients are analogousto the coefficients associated with the base functions.

Different transform algorithms can use different base patterns. Varioustransform algorithms can be used at transform stage 212, such as, forexample, a discrete cosine transform, a discrete sine transform, or thelike. The transform at transform stage 212 is invertible. That is, theencoder can restore residual BPU 210 by an inverse operation of thetransform (referred to as an “inverse transform”). For example, torestore a pixel of residual BPU 210, the inverse transform can bemultiplying values of corresponding pixels of the base patterns byrespective associated coefficients and adding the products to produce aweighted sum. For a video coding standard, both the encoder and decodercan use the same transform algorithm (thus the same base patterns).Thus, the encoder can record only the transform coefficients, from whichthe decoder can reconstruct residual BPU 210 without receiving the basepatterns from the encoder. Compared with residual BPU 210, the transformcoefficients can have fewer bits, but they can be used to reconstructresidual BPU 210 without significant quality deterioration. Thus,residual BPU 210 is further compressed.

The encoder can further compress the transform coefficients atquantization stage 214. In the transform process, different basepatterns can represent different variation frequencies (e.g., brightnessvariation frequencies). Because human eyes are generally better atrecognizing low-frequency variation, the encoder can disregardinformation of high-frequency variation without causing significantquality deterioration in decoding. For example, at quantization stage214, the encoder can generate quantized transform coefficients 216 bydividing each transform coefficient by an integer value (referred to asa “quantization scale parameter”) and rounding the quotient to itsnearest integer. After such an operation, some transform coefficients ofthe high-frequency base patterns can be converted to zero, and thetransform coefficients of the low-frequency base patterns can beconverted to smaller integers. The encoder can disregard the zero-valuequantized transform coefficients 216, by which the transformcoefficients are further compressed. The quantization process is alsoinvertible, in which quantized transform coefficients 216 can bereconstructed to the transform coefficients in an inverse operation ofthe quantization (referred to as “inverse quantization”).

Because the encoder disregards the remainders of such divisions in therounding operation, quantization stage 214 can be lossy. Typically,quantization stage 214 can contribute the most information loss inprocess 200A. The larger the information loss is, the fewer bits thequantized transform coefficients 216 can need. For obtaining differentlevels of information loss, the encoder can use different values of thequantization scale factor or any other parameter of the quantizationprocess.

At binary coding stage 226, the encoder can encode prediction data 206and quantized transform coefficients 216 using a binary codingtechnique, such as, for example, entropy coding, variable length coding,arithmetic coding, Huffman coding, context-adaptive binary arithmeticcoding, or any other lossless or lossy compression algorithm. In someembodiments, besides prediction data 206 and quantized transformcoefficients 216, the encoder can encode other information at binarycoding stage 226, such as, for example, a prediction mode used atprediction stage 204, parameters of the prediction operation, atransform type at transform stage 212, parameters of the quantizationprocess (e.g., quantization scale factors), an encoder control parameter(e.g., a bitrate control parameter), or the like. The encoder can usethe output data of binary coding stage 226 to generate video bitstream228. In some embodiments, video bitstream 228 can be further packetizedfor network transmission.

Referring to the reconstruction path of process 200A, at inversequantization stage 218, the encoder can perform inverse quantization onquantized transform coefficients 216 to generate reconstructed transformcoefficients. At inverse transform stage 220, the encoder can generatereconstructed residual BPU 222 based on the reconstructed transformcoefficients. The encoder can add reconstructed residual BPU 222 topredicted BPU 208 to generate prediction reference 224 that is to beused in the next iteration of process 200A.

It should be noted that other variations of the process 200A can be usedto encode video sequence 202. In some embodiments, stages of process200A can be performed by the encoder in different orders. In someembodiments, one or more stages of process 200A can be combined into asingle stage. In some embodiments, a single stage of process 200A can bedivided into multiple stages. For example, transform stage 212 andquantization stage 214 can be combined into a single stage. In someembodiments, process 200A can include additional stages. In someembodiments, process 200A can omit one or more stages in FIG. 2A.

FIG. 2B shows a schematic of another example encoding process, accordingto some embodiments of the present disclosure. As shown in FIG. 2B,process 200B can be modified from process 200A. For example, process200B can be used by an encoder conforming to a hybrid video codingstandard (e.g., H.26x series). Compared with process 200A, the forwardpath of process 200B additionally includes mode decision stage 230 anddivides prediction stage 204 into spatial prediction stage 2042 andtemporal prediction stage 2044. The reconstruction path of process 200Badditionally includes loop filter stage 232 and buffer 234.

Generally, prediction techniques can be categorized into two types:spatial prediction and temporal prediction. Spatial prediction (e.g., anintra-picture prediction or “intra prediction”) can use pixels from oneor more already coded neighboring BPUs in the same picture to predictthe current BPU. That is, prediction reference 224 in the spatialprediction can include the neighboring BPUs. The spatial prediction canreduce the inherent spatial redundancy of the picture. Temporalprediction (e.g., an inter-picture prediction or “inter prediction”) canuse regions from one or more already coded pictures to predict thecurrent BPU. That is, prediction reference 224 in the temporalprediction can include the coded pictures. The temporal prediction canreduce the inherent temporal redundancy of the pictures.

Referring to process 200B, in the forward path, the encoder performs theprediction operation at spatial prediction stage 2042 and temporalprediction stage 2044. For example, at spatial prediction stage 2042,the encoder can perform the intra prediction. For an original BPU of apicture being encoded, prediction reference 224 can include one or moreneighboring BPUs that have been encoded (in the forward path) andreconstructed (in the reconstructed path) in the same picture. Theencoder can generate predicted BPU 208 by extrapolating the neighboringBPUs. The extrapolation technique can include, for example, a linearextrapolation or interpolation, a polynomial extrapolation orinterpolation, or the like. In some embodiments, the encoder can performthe extrapolation at the pixel level, such as by extrapolating values ofcorresponding pixels for each pixel of predicted BPU 208. Theneighboring BPUs used for extrapolation can be located with respect tothe original BPU from various directions, such as in a verticaldirection (e.g., on top of the original BPU), a horizontal direction(e.g., to the left of the original BPU), a diagonal direction (e.g., tothe down-left, down-right, up-left, or up-right of the original BPU), orany direction defined in the used video coding standard. For the intraprediction, prediction data 206 can include, for example, locations(e.g., coordinates) of the used neighboring BPUs, sizes of the usedneighboring BPUs, parameters of the extrapolation, a direction of theused neighboring BPUs with respect to the original BPU, or the like.

For another example, at temporal prediction stage 2044, the encoder canperform the inter prediction. For an original BPU of a current picture,prediction reference 224 can include one or more pictures (referred toas “reference pictures”) that have been encoded (in the forward path)and reconstructed (in the reconstructed path). In some embodiments, areference picture can be encoded and reconstructed BPU by BPU. Forexample, the encoder can add reconstructed residual BPU 222 to predictedBPU 208 to generate a reconstructed BPU. When all reconstructed BPUs ofthe same picture are generated, the encoder can generate a reconstructedpicture as a reference picture. The encoder can perform an operation of“motion estimation” to search for a matching region in a scope (referredto as a “search window”) of the reference picture. The location of thesearch window in the reference picture can be determined based on thelocation of the original BPU in the current picture. For example, thesearch window can be centered at a location having the same coordinatesin the reference picture as the original BPU in the current picture andcan be extended out for a predetermined distance. When the encoderidentifies (e.g., by using a pel-recursive algorithm, a block-matchingalgorithm, or the like) a region similar to the original BPU in thesearch window, the encoder can determine such a region as the matchingregion. The matching region can have different dimensions (e.g., beingsmaller than, equal to, larger than, or in a different shape) from theoriginal BPU. Because the reference picture and the current picture aretemporally separated in the timeline (e.g., as shown in FIG. 1), it canbe deemed that the matching region “moves” to the location of theoriginal BPU as time goes by. The encoder can record the direction anddistance of such a motion as a “motion vector.” When multiple referencepictures are used (e.g., as picture 106 in FIG. 1), the encoder cansearch for a matching region and determine its associated motion vectorfor each reference picture. In some embodiments, the encoder can assignweights to pixel values of the matching regions of respective matchingreference pictures.

The motion estimation can be used to identify various types of motions,such as, for example, translations, rotations, zooming, or the like. Forinter prediction, prediction data 206 can include, for example,locations (e.g., coordinates) of the matching region, the motion vectorsassociated with the matching region, the number of reference pictures,weights associated with the reference pictures, or the like.

For generating predicted BPU 208, the encoder can perform an operationof “motion compensation.” The motion compensation can be used toreconstruct predicted BPU 208 based on prediction data 206 (e.g., themotion vector) and prediction reference 224. For example, the encodercan move the matching region of the reference picture according to themotion vector, in which the encoder can predict the original BPU of thecurrent picture. When multiple reference pictures are used (e.g., aspicture 106 in FIG. 1), the encoder can move the matching regions of thereference pictures according to the respective motion vectors andaverage pixel values of the matching regions. In some embodiments, ifthe encoder has assigned weights to pixel values of the matching regionsof respective matching reference pictures, the encoder can add aweighted sum of the pixel values of the moved matching regions.

In some embodiments, the inter prediction can be unidirectional orbidirectional. Unidirectional inter predictions can use one or morereference pictures in the same temporal direction with respect to thecurrent picture. For example, picture 104 in FIG. 1 is a unidirectionalinter-predicted picture, in which the reference picture (i.e., picture102) precedes picture 104. Bidirectional inter predictions can use oneor more reference pictures at both temporal directions with respect tothe current picture. For example, picture 106 in FIG. 1 is abidirectional inter-predicted picture, in which the reference pictures(i.e., pictures 104 and 108) are at both temporal directions withrespect to picture 104.

Still referring to the forward path of process 200B, after spatialprediction stage 2042 and temporal prediction stage 2044, at modedecision stage 230, the encoder can select a prediction mode (e.g., oneof the intra prediction or the inter prediction) for the currentiteration of process 200B. For example, the encoder can perform arate-distortion optimization technique, in which the encoder can selecta prediction mode to minimize a value of a cost function depending on abit rate of a candidate prediction mode and distortion of thereconstructed reference picture under the candidate prediction mode.Depending on the selected prediction mode, the encoder can generate thecorresponding predicted BPU 208 and predicted data 206.

In the reconstruction path of process 200B, if intra prediction mode hasbeen selected in the forward path, after generating prediction reference224 (e.g., the current BPU that has been encoded and reconstructed inthe current picture), the encoder can directly feed prediction reference224 to spatial prediction stage 2042 for later usage (e.g., forextrapolation of a next BPU of the current picture). The encoder canfeed prediction reference 224 to loop filter stage 232, at which theencoder can apply a loop filter to prediction reference 224 to reduce oreliminate distortion (e.g., blocking artifacts) introduced during codingof the prediction reference 224. The encoder can apply various loopfilter techniques at loop filter stage 232, such as, for example,deblocking, sample adaptive offsets, adaptive loop filters, or the like.The loop-filtered reference picture can be stored in buffer 234 (or“decoded picture buffer”) for later use (e.g., to be used as aninter-prediction reference picture for a future picture of videosequence 202). The encoder can store one or more reference pictures inbuffer 234 to be used at temporal prediction stage 2044. In someembodiments, the encoder can encode parameters of the loop filter (e.g.,a loop filter strength) at binary coding stage 226, along with quantizedtransform coefficients 216, prediction data 206, and other information.

FIG. 3A shows a schematic of an example decoding process, according tosome embodiments of the present disclosure. As shown in FIG. 3A, process300A can be a decompression process corresponding to the compressionprocess 200A in FIG. 2A. In some embodiments, process 300A can besimilar to the reconstruction path of process 200A. A decoder can decodevideo bitstream 228 into video stream 304 according to process 300A.Video stream 304 can be very similar to video sequence 202. However, dueto the information loss in the compression and decompression process(e.g., quantization stage 214 in FIGS. 2A-2B), generally, video stream304 is not identical to video sequence 202. Similar to processes 200Aand 200B in FIGS. 2A-2B, the decoder can perform process 300A at thelevel of basic processing units (BPUs) for each picture encoded in videobitstream 228. For example, the decoder can perform process 300A in aniterative manner, in which the decoder can decode a basic processingunit in one iteration of process 300A. In some embodiments, the decodercan perform process 300A in parallel for regions (e.g., regions 114-118)of each picture encoded in video bitstream 228.

In FIG. 3A, the decoder can feed a portion of video bitstream 228associated with a basic processing unit (referred to as an “encodedBPU”) of an encoded picture to binary decoding stage 302. At binarydecoding stage 302, the decoder can decode the portion into predictiondata 206 and quantized transform coefficients 216. The decoder can feedquantized transform coefficients 216 to inverse quantization stage 218and inverse transform stage 220 to generate reconstructed residual BPU222. The decoder can feed prediction data 206 to prediction stage 204 togenerate predicted BPU 208. The decoder can add reconstructed residualBPU 222 to predicted BPU 208 to generate predicted reference 224. Insome embodiments, predicted reference 224 can be stored in a buffer(e.g., a decoded picture buffer in a computer memory). The decoder canfeed predicted reference 224 to prediction stage 204 for performing aprediction operation in the next iteration of process 300A.

The decoder can perform process 300A iteratively to decode each encodedBPU of the encoded picture and generate predicted reference 224 forencoding the next encoded BPU of the encoded picture. After decoding allencoded BPUs of the encoded picture, the decoder can output the pictureto video stream 304 for display and proceed to decode the next encodedpicture in video bitstream 228.

At binary decoding stage 302, the decoder can perform an inverseoperation of the binary coding technique used by the encoder (e.g.,entropy coding, variable length coding, arithmetic coding, Huffmancoding, context-adaptive binary arithmetic coding, or any other losslesscompression algorithm). In some embodiments, besides prediction data 206and quantized transform coefficients 216, the decoder can decode otherinformation at binary decoding stage 302, such as, for example, aprediction mode, parameters of the prediction operation, a transformtype, parameters of the quantization process (e.g., quantization scalefactors), an encoder control parameter (e.g., a bitrate controlparameter), or the like. In some embodiments, if video bitstream 228 istransmitted over a network in packets, the decoder can depacketize videobitstream 228 before feeding it to binary decoding stage 302.

FIG. 3B shows a schematic of another example decoding process, accordingto some embodiments of the present disclosure. As shown in FIG. 3B,process 300B can be modified from process 300A. For example, process300B can be used by a decoder conforming to a hybrid video codingstandard (e.g., H.26x series). Compared with process 300A, process 300Badditionally divides prediction stage 204 into spatial prediction stage2042 and temporal prediction stage 2044, and additionally includes loopfilter stage 232 and buffer 234.

In process 300B, for an encoded basic processing unit (referred to as a“current BPU”) of an encoded picture (referred to as a “currentpicture”) that is being decoded, prediction data 206 decoded from binarydecoding stage 302 by the decoder can include various types of data,depending on what prediction mode was used to encode the current BPU bythe encoder. For example, if intra prediction was used by the encoder toencode the current BPU, prediction data 206 can include a predictionmode indicator (e.g., a flag value) indicative of the intra prediction,parameters of the intra prediction operation, or the like. Theparameters of the intra prediction operation can include, for example,locations (e.g., coordinates) of one or more neighboring BPUs used as areference, sizes of the neighboring BPUs, parameters of extrapolation, adirection of the neighboring BPUs with respect to the original BPU, orthe like. For another example, if inter prediction was used by theencoder to encode the current BPU, prediction data 206 can include aprediction mode indicator (e.g., a flag value) indicative of the interprediction, parameters of the inter prediction operation, or the like.The parameters of the inter prediction operation can include, forexample, the number of reference pictures associated with the currentBPU, weights respectively associated with the reference pictures,locations (e.g., coordinates) of one or more matching regions in therespective reference pictures, one or more motion vectors respectivelyassociated with the matching regions, or the like.

Based on the prediction mode indicator, the decoder can decide whetherto perform a spatial prediction (e.g., the intra prediction) at spatialprediction stage 2042 or a temporal prediction (e.g., the interprediction) at temporal prediction stage 2044. The details of performingsuch spatial prediction or temporal prediction are described in FIG. 2Band will not be repeated hereinafter. After performing such spatialprediction or temporal prediction, the decoder can generate predictedBPU 208. The decoder can add predicted BPU 208 and reconstructedresidual BPU 222 to generate prediction reference 224, as described inFIG. 3A.

In process 300B, the decoder can feed predicted reference 224 to spatialprediction stage 2042 or temporal prediction stage 2044 for performing aprediction operation in the next iteration of process 300B. For example,if the current BPU is decoded using the intra prediction at spatialprediction stage 2042, after generating prediction reference 224 (e.g.,the decoded current BPU), the decoder can directly feed predictionreference 224 to spatial prediction stage 2042 for later usage (e.g.,for extrapolation of a next BPU of the current picture). If the currentBPU is decoded using the inter prediction at temporal prediction stage2044, after generating prediction reference 224 (e.g., a referencepicture in which all BPUs have been decoded), the decoder can feedprediction reference 224 to loop filter stage 232 to reduce or eliminatedistortion (e.g., blocking artifacts). The decoder can apply a loopfilter to prediction reference 224, in a way as described in FIG. 2B.The loop-filtered reference picture can be stored in buffer 234 (e.g., adecoded picture buffer in a computer memory) for later use (e.g., to beused as an inter-prediction reference picture for a future encodedpicture of video bitstream 228). The decoder can store one or morereference pictures in buffer 234 to be used at temporal prediction stage2044. In some embodiments, prediction data can further includeparameters of the loop filter (e.g., a loop filter strength). In someembodiments, prediction data includes parameters of the loop filter whenthe prediction mode indicator of prediction data 206 indicates thatinter prediction was used to encode the current BPU.

There can be four types of loop filters. For example, the loop filterscan include a deblocking filter, a sample adaptive offsets (“SAO”)filter, a luma mapping with chroma scaling (“LMCS”) filter, and anadaptive loop filter (“ALF”). The order of applying the four types ofloop filters can be the LMCS filter, the deblocking filter, the SAOfilter, and the ALF. The LMCS filter can include two main components.The first component can be an in-loop mapping of the luma componentbased on adaptive piecewise linear models. The second component can befor the chroma components, and luma-dependent chroma residual scalingcan be applied.

FIG. 4 shows a block diagram of an example apparatus for encoding ordecoding a video, according to some embodiments of the presentdisclosure. As shown in FIG. 4, apparatus 400 can include processor 402.When processor 402 executes instructions described herein, apparatus 400can become a specialized machine for video encoding or decoding.Processor 402 can be any type of circuitry capable of manipulating orprocessing information. For example, processor 402 can include anycombination of any number of a central processing unit (or “CPU”), agraphics processing unit (or “GPU”), a neural processing unit (“NPU”), amicrocontroller unit (“MCU”), an optical processor, a programmable logiccontroller, a microcontroller, a microprocessor, a digital signalprocessor, an intellectual property (IP) core, a Programmable LogicArray (PLA), a Programmable Array Logic (PAL), a Generic Array Logic(GAL), a Complex Programmable Logic Device (CPLD), a Field-ProgrammableGate Array (FPGA), a System On Chip (SoC), an Application-SpecificIntegrated Circuit (ASIC), or the like. In some embodiments, processor402 can also be a set of processors grouped as a single logicalcomponent. For example, as shown in FIG. 4, processor 402 can includemultiple processors, including processor 402 a, processor 402 b, andprocessor 402 n.

Apparatus 400 can also include memory 404 configured to store data(e.g., a set of instructions, computer codes, intermediate data, or thelike). For example, as shown in FIG. 4, the stored data can includeprogram instructions (e.g., program instructions for implementing thestages in processes 200A, 200B, 300A, or 300B) and data for processing(e.g., video sequence 202, video bitstream 228, or video stream 304).Processor 402 can access the program instructions and data forprocessing (e.g., via bus 410), and execute the program instructions toperform an operation or manipulation on the data for processing. Memory404 can include a high-speed random-access storage device or anon-volatile storage device. In some embodiments, memory 404 can includeany combination of any number of a random-access memory (RAM), aread-only memory (ROM), an optical disc, a magnetic disk, a hard drive,a solid-state drive, a flash drive, a security digital (SD) card, amemory stick, a compact flash (CF) card, or the like. Memory 404 canalso be a group of memories (not shown in FIG. 4) grouped as a singlelogical component.

Bus 410 can be a communication device that transfers data betweencomponents inside apparatus 400, such as an internal bus (e.g., aCPU-memory bus), an external bus (e.g., a universal serial bus port, aperipheral component interconnect express port), or the like.

For ease of explanation without causing ambiguity, processor 402 andother data processing circuits are collectively referred to as a “dataprocessing circuit” in this disclosure. The data processing circuit canbe implemented entirely as hardware, or as a combination of software,hardware, or firmware. In addition, the data processing circuit can be asingle independent module or can be combined entirely or partially intoany other component of apparatus 400.

Apparatus 400 can further include network interface 406 to provide wiredor wireless communication with a network (e.g., the Internet, anintranet, a local area network, a mobile communications network, or thelike). In some embodiments, network interface 406 can include anycombination of any number of a network interface controller (NIC), aradio frequency (RF) module, a transponder, a transceiver, a modem, arouter, a gateway, a wired network adapter, a wireless network adapter,a Bluetooth adapter, an infrared adapter, an near-field communication(“NFC”) adapter, a cellular network chip, or the like.

In some embodiments, apparatus 400 can further include peripheralinterface 408 to provide a connection to one or more peripheral devices.As shown in FIG. 4, the peripheral device can include, but is notlimited to, a cursor control device (e.g., a mouse, a touchpad, or atouchscreen), a keyboard, a display (e.g., a cathode-ray tube display, aliquid crystal display, or a light-emitting diode display), a videoinput device (e.g., a camera or an input interface communicativelycoupled to a video archive), or the like.

It should be noted that video codecs (e.g., a codec performing process200A, 200B, 300A, or 300B) can be implemented as any combination of anysoftware or hardware modules in apparatus 400. For example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore software modules of apparatus 400, such as program instructionsthat can be loaded into memory 404. For another example, some or allstages of process 200A, 200B, 300A, or 300B can be implemented as one ormore hardware modules of apparatus 400, such as a specialized dataprocessing circuit (e.g., an FPGA, an ASIC, an NPU, or the like).

In the quantization and inverse quantization functional blocks (e.g.,quantization 214 and inverse quantization 218 of FIG. 2A or FIG. 2B,inverse quantization 218 of FIG. 3A or FIG. 3B), a quantizationparameter (QP) is used to determine the amount of quantization (andinverse quantization) applied to the prediction residuals. Initial QPvalues used for coding of a picture or slice can be signaled at the highlevel, for example, using init_qp_minus26 syntax element in the PictureParameter Set (PPS) and using slice_qp_delta syntax element in the sliceheader. Further, the QP values can be adapted at the local level foreach CU using delta QP values sent at the granularity of quantizationgroups.

An Equirectangular Projection (“ERP”) format is a common projectionformat used to represent 360-degree videos and images. The projectionmaps meridians to vertical straight lines of constant spacing, andcircles of latitude to horizontal straight lines of constant spacing.Because the particularly simple relationship between the position of animage pixel on the map and its corresponding geographic location onsphere, ERP is one of the most common projections used for 360-degreevideos and images.

Algorithm description of projection format conversion and video qualitymetrics output by JVET gives the introduction and coordinate conversionbetween ERP and sphere. For 2D-to-3D coordinate conversion, given asampling position (m, n), (u, v) can be calculated based on thefollowing equations (1) and (2).

u=(m+0.5)/W,0≤m<W  Eq. (1)

v=(n+0.5)/H,0≤n<H  Eq. (2)

Then, the longitude and latitude (4, 0) in the sphere can be calculatedfrom (u, v) based on the following equations (3) and (4).

ϕ=(u−0.5)×(2×π)  Eq. (3)

θ=(0.5−v)×π  Eq. (4)

3D Coordinates (X, Y, Z) can be calculated based on the followingequations (5)-(7).

X=cos(θ)cos(ϕ)  Eq. (5)

Y=sin(θ)  Eq. (6)

Z=−cos(θ)sin(ϕ)  Eq. (7)

For 3D-to-2D coordinate conversion starting from (X, Y, Z), (ϕ, θ) canbe calculated based on the following equations (8) and (9). Then, (u, v)is calculated based on equations (3) and (4). Finally, 2D coordinates(m, n) can be calculated based on equations (1) and (2).

ϕ=tan⁻¹(−Z/X)  Eq. (8)

θ=sin⁻¹(Y/(X ² +Y ² +Z ²)^(1/2))  Eq. (9)

To reduce the seam artifacts in reconstructed viewports that encompassthe left and right boundaries of the ERP picture, a new format calledpadded equirectangular projection (“PERP”) is provided by paddingsamples on each of the left and the right sides of the ERP picture.

When PERP is used to represent the 360-degree videos, the PERP pictureis encoded. After decoding, the reconstructed PERP is converted back toreconstructed ERP by blending the duplicated samples or cropping thepadded areas.

FIG. 5A shows a schematic of an example blending operation forgenerating reconstructed equirectangular projections, according to someembodiments of the present disclosure. Unless otherwise stated,“recPERP” is used to denote the reconstructed PERP before thepost-processing, and “recERP” is used to denote the reconstructed ERPafter the post-processing. In FIG. 5A, A1 and B2 are boundary areaswithin ERP picture, and B1 and A2 are padded areas where A2 is paddedfrom A1 and B1 is padded from B2. As shown in FIG. 5A, the duplicatedsamples of the recPERP can be blended by applying a distance-basedweighted averaging operation. For example, region A can be generated byblending regions A1 with A2, and region B is generated by blendingregions B1 with B2.

In the following description, the width and height of unpadded recERPare denoted as “W” and “H” respectively. The left and right paddingwidths are denoted as “P_(L)” and “P_(R)” respectively. The totalpadding width is denoted as “P_(W),” which can be a sum of P_(L) andP_(R).

In some embodiments, recPERP can be converted to recERP via blendingoperations. For example, for a sample recERP(j, i) in A where (j,i) isthe coordinate in ERP picture and i is in [0, P_(R)−1] and j is in [0,H−1], recERP (j, i) can be determined according to the followingequations.

A=w×A1+(1−w)×A2, where w is from P _(L) /P _(W) to 1  Eq. (10)

recERP(j,i) in A=(recPERP(j,i+P _(L))×(i+P _(L))+recPERP(j,i+P _(L)+W)×(P _(R) −i)+(P _(W)>>1))/P _(W)  Eq. (11)

where recPERP(y, x) is a sample on reconstructed PERP picture with (y,x) being the coordinate of the sample in PREP picture.

In some embodiments, for a sample recERP(j, i) in B where (j,i) is thecoordinate in ERP picture and i is in [W−P_(L), W−1] and j is in [0,H−1], recERP (j, i) can be generated according to the followingequations.

B=k×B1+(1−k)×B2, where k is from 0 to P _(L) /P _(W)  Eq. (12)

recERP(j,i) in B=(recPERP(j,i+P _(L))×(P _(R) −i+W)+recPERP(j,i+P _(L)−w)×(i−W+P _(L))+(P _(W)>>1))/P _(W)  Eq. (13)

where recPERP(y, x) is a sample on reconstructed PERP picture with (y,x) is the coordinate of the sample in PREP picture

FIG. 5B shows schematic of an example cropping operation for generatingreconstructed equirectangular projections, according to some embodimentsof the present disclosure. In FIG. 5B, A1 and B2 are boundary areaswithin ERP picture, and B1 and A2 are padded areas where A2 is paddedfrom A1 and B1 is padded from B2. As shown in FIG. 5B, during thecropping process, the padded samples in recPERP can be directlydiscarded to obtain recERP. For example, padded samples B1 and A2 can bediscarded.

In some embodiments, horizontal wrap-around motion compensation can beused to improve the coding performance of ERP. For example, thehorizontal wrap-around motion compensation can be used in the VVCstandard as a 360-specific coding tool designed to improve the visualquality of reconstructed 360-degree video in the ERP format or PERPformat. In a conventional motion compensation, when a motion vectorrefers to samples beyond the picture boundaries of the referencepicture, repetitive padding is applied to derive the values of theout-of-bounds samples by copying from those nearest neighbors on thecorresponding picture boundary. For 360-degree video, this method ofrepetitive padding is not suitable, and could cause visual artefactscalled “seam artefacts” in a reconstructed viewport video. Because a360-degree video is captured on a sphere and inherently has no“boundary,” the reference samples that are out of the boundaries of areference picture in the projected domain can be obtained fromneighboring samples in the spherical domain. For a general projectionformat, it may be difficult to derive the corresponding neighboringsamples in the spherical domain, because it involves 2D-to-3D and3D-to-2D coordinate conversion, as well as sample interpolation forfractional sample positions. This problem can be resolved for the leftand right boundaries of the ERP or PERP projection format, as thespherical neighbors outside of the left picture boundary can be obtainedfrom samples inside the right picture boundary, and vice versa. Giventhe wide usage of the ERP or PERP projection format, and the relativeease of implementation, the horizontal wrap-around motion compensationwas adopted to VVC to improve the visual quality of 360-degree videocoded in the ERP or PERP projection format.

FIG. 6A shows a schematic of an example horizontal wrap-around motioncompensation process for equirectangular projections, according to someembodiments of the present disclosure. As shown in FIG. 6A, when a partof the reference block is outside of the reference picture's left (orright) boundary in the projected domain, instead of repetitive padding,the “out-of-boundary” part can be taken from the corresponding sphericalneighbors that are located within the reference picture toward the right(or left) boundary in the projected domain. In some embodiments,repetitive padding may be used for the top and bottom pictureboundaries.

FIG. 6B shows a schematic of an example horizontal wrap-around motioncompensation process for padded equirectangular projections, accordingto some embodiments of the present disclosure. As shown in FIG. 6B, thehorizontal wrap-around motion compensation can be combined with anon-normative padding method that is often used in 360-degree videocoding. In some embodiments, this is achieved by signaling a high-levelsyntax element to indicate the wrap-around motion compensation offset,which can be set to the ERP picture width before padding. This syntaxcan be used to adjust the position of horizontal wrap-aroundaccordingly. In some embodiments, this syntax is not affected by aspecific amount of padding on the left or right picture boundaries. As aresult, this syntax can naturally support asymmetric padding of the ERPpicture. In the asymmetric padding of the ERP picture, the left andright paddings can be different. In some embodiments, the wrap-aroundmotion compensation can be determined according to the followingequation:

$\begin{matrix}{{{pos}_{x}{\_ wrap}} = \{ \begin{matrix}{{{pos}_{x} + {offset}};} & {{pos}_{x} < 0} \\{{{pos}_{x} - {offset}};} & {{pos}_{x} > {{picW} - 1}} \\{{pos}_{x};} & {otherwise}\end{matrix} } & {{Eq}.\mspace{14mu}(14)}\end{matrix}$

where the offset can be a wrap-around motion compensation offsetsignaled in the bitstream, picW can be a picture width including thepadding area before encoding, pos_(x) can be a reference positiondetermined by current block position and the motion vector, and theoutput of the equation pos_(x)_wrap can be an actual reference positionwhere the reference block is from in the wrap-around motioncompensation. To save the signaling overhead of the wrap-around motioncompensation offset, it can be in unit of minimum luma coding block,thus the offset can be replaced with offset_(w)×MinCbSizeY whereoffset_(w) is the wrap-around motion compensation offset in unit ofminimum luma coding block which is signaled in the bitstream andMinCbSizeY is the size of minimum luma coding block. In contrast, in atraditional motion compensation, the actual reference position where thereference block is from may be directly derived by clipping pos_(x)within 0 to picW−1.

The horizontal wrap-around motion compensation can provide moremeaningful information for motion compensation when the referencesamples are outside of the reference picture's left and rightboundaries. Under the 360-degree video common test conditions, this toolcan improve compression performance not only in terms ofrate-distortion, but also in terms of reduced seam artefacts andsubjective quality of the reconstructed 360-degree video. The horizontalwrap-around motion compensation can also be used for other single faceprojection formats with constant sampling density in the horizontaldirection, such as adjusted equal-area projection.

In VVC, (e.g., VVC draft 8), the wrap-around motion compensation can beachieved by signaling a high-level syntax variablepps_ref_wraparound_offset to indicate the wrap-around offset. Sometimes,the wrap-around offset should be set to the ERP picture width beforepadding. This syntax can be used to adjust the position of horizontalwrap-around motion compensation accordingly. This syntax may not beaffected by the specific amount of padding on the left or right pictureboundaries. As a result, this syntax can naturally support asymmetricpadding of the ERP picture (e.g., when left and right padding aredifferent). The horizontal wrap-around motion compensation can providemore meaningful information for motion compensation when the referencesamples are outside of the reference picture's left and rightboundaries.

FIG. 7 shows syntax of an example high level wrap-around offset,according to some embodiments of the present disclosure. It isappreciated that the syntax shown in FIG. 7 can be used in VVC (e.g.,VVC draft 8). As shown in FIG. 7, when the wrap-around motioncompensation is enabled (e.g., pps_ref_wraparound_enabled_flag=1), thewrap-around offset pps_ref_wraparound_offset can be directly signaled.As shown in FIG. 7, syntax elements or variables in a bitstream areshown in bold.

FIG. 8 shows semantics of an example high level wrap-around offset,according to some embodiments of the present disclosure. It isappreciated that the semantics shown in FIG. 8 can correspond to thesyntax shown in FIG. 7. In some embodiments, as shown in FIG. 8,pps_ref_wraparound_enabled_flag having a value of 1 means that thehorizontal wrap-around motion compensation is applied in interprediction. If pps_ref_wraparound_enabled_flag has a value of 0,horizontal wrap-around motion compensation is not applied. When thevalue of CtbSizeY/MinCbSizeY+1 is greater thanpic_width_in_luma_samples/MinCbSizeY−1, the value ofpps_ref_wraparound_enabled_flag should be equal to 0. Whensps_ref_wraparound_enabled_flag is equal to 0, the value ofpps_ref_wraparound_enabled_flag should be equal to 0. CtbSizeY is thesize of the luma coding tree block.

In some embodiments, as shown in FIG. 8, the value ofpps_ref_wraparound_offset plus (CtbSizeY/MinCbSizeY)+2 can specify theoffset used for computing the horizontal wrap-around position in unitsof MinCbSizeY luma samples. The value of pps_ref_wraparound_offset canbe in the range of 0 to(pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,inclusive. A variable PpsRefWraparoundOffset can be set to be equal topps_ref_wraparound_offset+(CtbSizeY/MinCbSizeY)+2. In some embodiments,variable PpsRefWraparoundOffset can be used to determine a luma locationof a subblock (e.g., in VVC Draft 8).

In VVC (e.g., VVC draft 8), a picture can be divided into one or moretile rows or one or more tile columns. A tile can be a sequence ofcoding tree units (“CTUs”) that covers a rectangular region of apicture. A slice can comprise an integer number of complete tiles or aninteger number of consecutive complete CTU rows within a tile of apicture.

Two modes of slices can be supported, namely a raster-scan slice modeand a rectangular slice mode. In the raster-scan slice mode, a slice cancomprise a sequence of complete tiles in a tile raster scan of apicture. In the rectangular slice mode, a slice can comprise either anumber of complete tiles that collectively form a rectangular region ofthe picture, or a number of consecutive complete CTU rows of one tilethat collectively form a rectangular region of the picture. Tiles withina rectangular slice are scanned in tile raster scan order within therectangular region corresponding to that slice.

A subpicture can comprise one or more slices that collectively cover arectangular region of a picture. FIG. 9 shows a schematic of an exampleslice and subpicture partitioning of a picture, according to someembodiments of the present disclosure. As shown in FIG. 9, the pictureis partitioned into 20 tiles, with 5 tile columns and 4 tile rows. Thereare 12 tiles on the left side, each covering one slice of 4 by 4 CTUs.There are 8 tiles on the right side, each covering 2 vertically stackedslices of 2 by 2 CTUs. Altogether, there are 28 slices and 28subpictures of varying dimensions (e.g., each slice can be asubpicture).

FIG. 10 shows a schematic of an example slice and subpicturepartitioning of a picture having different slices and subpictures,according to some embodiments of the present disclosure. As shown inFIG. 10, the picture is partitioned into 20 tiles, with 5 tile columnsand 4 tile rows. There are 12 tiles on the left, each covering one sliceof 4 by 4 CTUs. There are 8 tiles on the right, each covering 2vertically stacked slices of 2 by 2 CTUs. Altogether, there are 28slices. For the 12 slices on the left, each slice is a subpicture. Forthe 16 slices on the right, each 4 slices form a subpicture. As aresult, altogether there are 16 subpictures with same dimension.

In VVC (e.g., VVC draft 8), information regarding slice layouts can besignaled in a picture parameter set (“PPS”). In some embodiments, thepicture parameter set is a syntax structure including syntax elements orvariables that apply to zero or more entire coded pictures as determinedby a syntax element found in each picture header. FIG. 11 shows syntaxof an example picture parameter set for tile mapping and slice layouts,according to some embodiments of the present disclosure. It isappreciated that the syntax shown in FIG. 11 can be used in VVC (e.g.,VVC draft 8). As shown in FIG. 11, syntax elements or variables in abitstream are shown in bold. As shown in FIG. 11, if a number of tilesin a current picture is larger than 1 and the rectangular slice mode(e.g., rect_slice_flag==1) is used, a flag calledsingle_slice_per_subpic_flag can be signaled first to indicate that eachsubpicture includes only one slice. In this case (e.g.,single_slice_per_subpic_flag=1), there is no need to further signal thelayout information of the slice, since it may be the same as thesubpicture layout which is already signaled in a sequence parameter set(“SPS”). In some embodiments, the SPS is a syntax structure thatincludes syntax elements applied to zero or more entire coded layervideo sequences (“CLVSs”) as determined by the content of a syntaxelement found in a picture parameter set referred to by a syntax elementfound in each picture header. In some embodiments, the picture header isa syntax structure that includes syntax elements that apply to allslices of a coded picture. In some embodiments, as shown in FIG. 11, ifsingle_slice_per_subpic_flag has a value of 0, the number of slices inthe picture (e.g., num_slices_in_pic_minus1) can be signaled firstfollowed by the slice position and dimension information for each slice.

In some embodiments, to signal the number of slices, slice number minus1 (e.g., num_slices_in_pic_minus1) can be signaled instead of directlysignaling the slice number, since there is at least 1 slice in apicture. Generally, signaling a smaller positive value can cost fewerbits and improve overall efficiency of executing the video processing.

FIG. 12 shows semantics of an example picture parameter set for tilemapping and slice layouts, according to some embodiments of the presentdisclosure. It is appreciated that the semantics shown in FIG. 12 cancorrespond to the syntax shown in FIG. 11. In some embodiments,semantics shown in FIG. 12 corresponds to VVC (e.g., VVC draft 8).

In some embodiments, as shown in FIG. 12, variable rect_slice_flag beingequal to 0 means that tiles within each slice are in the raster scanorder, and the slice information is not signaled in PPS. When variablerect_slice_flag is equal to 1, tiles within each slice can cover arectangular region of the picture and the slice information can besignaled in the PPS. In some embodiments, when not present, variablerect_slice_flag can be inferred to be equal to 1. In some embodiments,when variable subpic_info_present_flag is equal to 1, the value ofrect_slice_flag should be equal to 1.

In some embodiments, as shown in FIG. 12, variablesingle_slice_per_subpic_flag being equal to 1 mean that each subpicturecan comprise one and only one rectangular slice. When variablesingle_slice_per_subpic_flag is equal to 0, each subpicture may compriseone or more rectangular slices. In some embodiments, when variablesingle_slice_per_subpic_flag is equal to 1, variablenum_slices_in_pic_minus1 can be inferred to be equal to variablesps_num_subpics_minus1. In some embodiments, when not present, the valueof single_slice_per_subpic_flag can be inferred to be equal to 0.

In some embodiments, as shown in FIG. 12, variablenum_slices_in_pic_minus1 plus 1 is the number of rectangular slices ineach picture referring to the PPS. In some embodiments, the value ofnum_slices_in_pic_minus1 can be in the range of 0 toMaxSlicesPerPicture−1, inclusive. In some embodiments, when variableno_pic_partition_flag is equal to 1, the value ofnum_slices_in_pic_minus1 can be inferred to be equal to 0.

In some embodiments, as shown in FIG. 12, if variabletile_idx_delta_present_flag is equal to 0, values of tile_idx_delta arenot present in the PPS, and all rectangular slices in pictures referringto the PPS are specified in raster order. In some embodiments, whenvariable tile_idx_delta_present_flag is equal to 1, values oftile_idx_delta may be present in the PPS, and all rectangular slices inpictures referring to the PPS are specified in the order indicated bythe values of tile_idx_delta. In some embodiments, when not present, thevalue of tile_idx_delta_present_flag can be inferred to be equal to 0.

In some embodiments, as shown in FIG. 12, variableslice_width_in_tiles_minus1[i] plus 1 specifies the width of the i-threctangular slice in units of tile columns. In some embodiments, thevalue of slice_width_in_tiles_minus1[i] should be in the range of 0 toNumTileColumns−1, inclusive. In some embodiments, ifslice_width_in_tiles_minus1[i] is not present, the following can apply:if NumTileColumns is equal to 1, the value ofslice_width_in_tiles_minus1[i] can be inferred to be equal to 0;otherwise, the value of slice_width_in_tiles_minus_1[i] can be inferredas specified in a clause in VVC draft (e.g., VVC draft 8).

In some embodiments, as shown in FIG. 12, variableslice_height_in_tiles_minus1 plus 1 specifies the height of the i-threctangular slice in units of tile rows. In some embodiments, the valueof slice_height_in_tiles_minus1[i] should be in the range of 0 toNumTileRows−1, inclusive. In some embodiments, when variableslice_height_in_tiles_minus1[i] is not present, the following applies:if NumTileRows is equal to 1, or variable tile_idx_delta_present_flag isequal to 0 and tileIdx % NumTileColumns is greater than 0, the value ofslice_height_in_tiles_minus1[i] is inferred to be equal to 0; otherwise(e.g., NumTileRows is not equal to 1, and tile_idx_delta_present_flag isequal to 1 or tileIdx % NumTileColumns is equal to 0), whentile_idx_delta_present_flag is equal to 1 or tileIdx % NumTileColumns isequal to 0, the value of slice_height_in_tiles_minus1[i] can be inferredto be equal to slice_height_in_tiles_minus1[i−1].

In some embodiments, as shown in FIG. 12, the value ofnum_exp_slices_in_tile[i] specifies the number of explicitly providedslice heights in the current tile that comprises more than onerectangular slice. In some embodiments, the value ofnum_exp_slices_in_tile[i] should be in the range of 0 toRowHeight[tileY]−1, inclusive, where tileY is the tile row indexcomprising the i-th slice. In some embodiments, when not present, thevalue of num_exp_slices_in tile[i] can be inferred to be equal to 0. Insome embodiments, when num_exp_slices_in_tile[i] is equal to 0, thevalue of the variable NumSliceInTile[i] is derived to be equal to 1.

In some embodiments, as shown in FIG. 12, the value ofexp_slice_height_in_ctus_minus1[j] plus 1 specifies the height of thej-th rectangular slice in the current tile in units of CTU rows. In someembodiments, the value of exp_slice_height_in_ctus_minus1[j] should bein the range of 0 to RowHeight[tileY]−1, inclusive, where tileY is thetile row index of the current tile.

In some embodiments, as shown in FIG. 12, when variablenum_exp_slices_in_tile[i] is greater than 0, variable NumSlicesInTile[i]and SliceHeightInCtusMinus1[i+k] for k in the range of 0 toNumSlicesInTile[i]−1 can be derived. In some embodiments, as shown inFIG. 8, values of NumSlicesInTile[i] and SliceHeightInCtusMinus1[i+k]can be derived when the value of num_exp_slices_in tile[i] is greaterthan 0.

In some embodiments, as shown in FIG. 12, the value of tile_idx_delta[i]specifies the difference between the tile index of the first tile in thei-th rectangular slice and the tile index of the first tile in the(i+1)-th rectangular slice. The value of tile_idx_delta[i] should be inthe range of −NumTilesInPic+1 to NumTilesInPic−1, inclusive. In someembodiments, when not present, the value of tile_idx_delta[i] can beinferred to be equal to 0. In some embodiments, when present, the valueof tile_idx_delta[i] can be inferred to not be equal to 0.

In VVC (e.g., VVC draft 8), to locate each slice in the picture, one ormore slice addresses can be signaled in slice header. FIG. 13 showssyntax of an example slice header, according to some embodiments of thepresent disclosure. It is appreciated that the syntax shown in FIG. 13can be used in VVC (e.g., VVC draft 8). As shown in FIG. 11, syntaxelements or variables in a bitstream are shown in bold. As shown in FIG.13, if variable picture_header_in_slice_header_flag is equal to 1, thepicture header syntax structure is present in the slice header.

FIG. 14 shows semantics of an example slice header, according to someembodiments of the present disclosure. It is appreciated that thesemantics shown in FIG. 14 can correspond to the syntax shown in FIG.13. In some embodiments, semantics shown in FIG. 14 corresponds to VVC(e.g., VVC draft 8).

In some embodiments, as shown in FIG. 14, it is a requirement ofbitstream conformance that the value ofpicture_header_in_slice_header_flag should be the same in all codedslices in a CLVS.

In some embodiments, as shown in FIG. 14, when variablepicture_header_in_slice_header_flag is equal to 1 for a coded slice, itis a requirement of bitstream conformance that no video coding layer(“VCL”) network abstraction layer (“NAL”) unit with nal_unit_type equalto PH_NUT should be present in the CLVS.

In some embodiments, as shown in FIG. 14, whenpicture_header_in_slice_header_flag is equal to 0, all coded slices inthe current picture should have picture_header_in_slice_header_flagbeing equal to 0, and the current PU should have a PH NAL unit.

In some embodiments, as shown in FIG. 14, variable slice_address canspecify the slice address of the slice. In some embodiments, when notpresent, the value of slice_address can be inferred to be equal to 0.When variable rect_slice_flag is equal to 1 andNumSliceInSubpic[CurrSubpicIdx] is equal to 1, the value ofslice_address is inferred to be equal to 0.

In some embodiments, as shown in FIG. 14, if variable rect_slice_flag isequal to 0, the following can apply: the slice address can be the rasterscan tile index; the length of slice_address can be ceil (Log 2(NumTilesInPic)) bits; and the value of slice_address should be in therange of 0 to NumTilesInPic−1, inclusive.

In some embodiments, as shown in FIG. 14, it is a requirement ofbitstream conformance that the following constrains apply: if variablerect_slice_flag is equal to 0 or variable subpic_info_present_flag isequal to 0, the value of slice_address should not be equal to the valueof slice_address of any other coded slice NAL unit of the same codedpicture; otherwise, the pair of slice_subpic_id and slice_address valuesshould not be equal to the pair of slice_subpic_id and slice_addressvalues of any other coded slice NAL unit of the same coded picture.

In some embodiments, as shown in FIG. 14, the shapes of the slices of apicture should be such that each CTU, when decoded, should have itsentire left boundary and entire top boundary including a pictureboundary or including boundaries of previously decoded CTU(s).

In some embodiments, as shown in FIG. 14, variable slice_address mayonly be signaled if one of the following two conditions are satisfied:rectangular slice mode is used and a number of slice(s) in currentsubpicture is larger than 1; or rectangular slice mode is not used andthe number of tiles in current picture is larger than 1. In someembodiments, if none of the above two conditions are satisfied, there isonly one slice either in current subpicture or current picture. In thatcase, there is no need to signal the slice address since the wholesubpicture or the whole picture is single slice.

There are many issues with the current design of the VVC. First, thewraparound offset pps_ref_wraparound_offset is signaled in bitstream,and it should be set to ERP picture width before padding. To save bits,the minimum value of wraparound offset (e.g., CtbSizeY/MinCbSizeY)+2) issubtracted from the wraparound offset before signaling. However, thewidth of the padding area is much less than the width of the originalERP picture. This is especially true for coding ERP pictures where thewidth of padding area can be 0. Given that the total width of thepicture to be encoded or decoded is known, signaling width of theoriginal ERP part can cost more bits than signaling width of the paddingarea. As a result, the current signaling of wraparound offset whichsignals the original ERP width in units of MinCbSizeY is not efficient.

Moreover, the slice layout signaling can also be improved. For example,1 is subtracted from the number of slices before signaling the number ofslices, since the number of slices in a picture is always larger than orequal to one, and signaling a smaller positive value takes fewer bits.However, in the current VVC (e.g., VVC draft 8), a subpicture includesan integer number of complete slices. As a result, the number of slicesin a picture is larger than or equal to the number of subpictures in apicture. In the current VVC (e.g., VVC draft 8), thenum_slices_in_pic_minus1 is only signaled when variablesingle_slice_per_subpic_flag is 0, and variablesingle_slice_per_subpic_flag being equal to 0 means there is at leastone subpicture containing more than one slice. So in this case, theslice number must be larger than the subpicture number of which theminimum value is one. As a result, the minimum value ofnum_slices_in_pic_minus1 is larger than zero. Signaling a non-negativevalue whose range is not from zero is not efficient.

Furthermore, there are other issues with the slice address signaling.When there is only one slice in the current picture, there may not be aneed to signal slice address, since the whole subpicture or the wholepicture is a single slice. The slice address can be inferred to be 0.However, the two conditions to skip the slice address signaling are notcomplete. For example, in the raster-scan slice mode, even the number oftiles is larger than one, there can be only one slice which includes allthe tiles in the picture, in which case slice address signaling can beavoided as well.

Embodiments of the present disclosure provide methods to combat theissues described above. In some embodiments, since the width of thepadding area is usually less than the width of the original ERP picturewhich may be the same as the wraparound offset in the wrap-around motioncompensation, it can be proposed to signal a difference between thecoded picture width and the original ERP picture width in the bitstream.For example, it can be proposed to signal a difference between the codedpicture width and the wrap-around motion compensation offset in thebitstream and to perform a deduction after parsing the signaleddifference to get the wraparound offset on the decoder side. Since thedifference between the coded picture width and the wraparound offset isusually less than the wraparound offset itself, this method can savesignaled bits.

FIG. 15 shows syntax of an example improved picture parameter set,according to some embodiments of the present disclosure. As shown inFIG. 15, syntax elements or variables in a bitstream are shown in bold,and changes from the previous VVC (e.g., syntax shown in FIG. 7) areshown in italic type, with proposed deleted syntax being further shownin strikethrough. As shown in FIG. 15, a new variablepps_pic_width_minus_wraparound_offset can be created. The value ofvariable pps_pic_width_minus_wraparound_offset can be signaled accordingto the value of pps_ref_wraparound_enabled_flag. In some embodiments,new variable pps_pic_width_minus_wraparound_offset can replace variablepps_ref_wraparound_offset in the original VVC (e.g., VVC draft 8).

FIG. 16 shows semantics of an example improved picture parameter set,according to some embodiments of the present disclosure. As shown inFIG. 16, changes from the previous VVC (e.g., semantics shown in FIG. 8)are shown in italic type, with proposed deleted syntax being furthershown in strikethrough. It is appreciated that the semantics shown inFIG. 16 can correspond to the syntax shown in FIG. 15. In someembodiments, semantics shown in FIG. 16 corresponds to VVC (e.g., VVCdraft 8).

As shown in FIG. 16, the semantics for the new variablepps_pic_width_minus_wraparound_offset is different from variablepps_ref_wraparound_offset (e.g., as shown in FIG. 8). Variablepps_pic_width_minus_wraparound_offset can specify the difference betweenthe picture width and the offset used for computing the horizontalwrap-around position in units of MinCbSizeY luma samples. In someembodiments, as shown in FIG. 16, the value ofpps_pic_width_minus_wraparound_offset should be less than or equal to(pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2. In someembodiments, the variable PpsRefWraparoundOffset can be set to be equaltopic_width_in_luma_samples/MinCbSizeY−pps_pic_width_minus_wraparound_offset.

In some embodiments, a flag wraparound_offset_type can be signaled toindicate whether the signaled wraparound offset value is the originalERP picture width or the difference between the coded picture width andthe original ERP picture width. The encoder may select the a smaller onefrom these two values and signal it in the bitstream, so that thesignaling overhead may be further reduced. FIG. 17 shows syntax of anexample picture parameter set with a variable wraparound_offset_type,according to some embodiments of the present disclosure. As shown inFIG. 17, syntax elements or variables in a bitstream are shown in bold,and changes from the previous VVC (e.g., syntax shown in FIG. 7) areshown in italic type. As shown in FIG. 17, a new variablepps_ref_wraparound_offset can be added to specify the value used todetermine PpsRefWraparoundOffset.

FIG. 18 shows semantics of an example improved picture parameter setwith a variable wraparound_offset_type, according to some embodiments ofthe present disclosure. As shown in FIG. 18, changes from the previousVVC (e.g., semantics shown in FIG. 8) are shown in italic type, withproposed deleted syntax being further shown in strikethrough. It isappreciated that the semantics shown in FIG. 18 can correspond to thesyntax shown in FIG. 17. In some embodiments, semantics shown in FIG. 18corresponds to VVC (e.g., VVC draft 8).

In some embodiments, as shown in FIG. 18, a new variablewraparound_offset_type can be added to specify the type of variablepps_ref_wraparound_offset.

The value of pps_ref_wraparound_offset should be in the range of 0 to((pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2)/2.

In some embodiments, as shown in FIG. 18, the value of variablePpsRefWraparoundOffset can be derived. For example, when variablewraparound_offset_type is equal to 0, the signaled wraparound offsetvalue is the original ERP picture width. As a result, variablePpsRefWraparoundOffset is equal topps_ref_wraparound_offset+(CrbSizeY/MinCbSizeY)+2. When variablewraparound_offset_type is not equal to 0, the signaled wraparound offsetvalue is the difference between the coded picture width and the originalERP picture width. As a result, variable PpsRefWraparoundOffset is equalto pps_pic_width_in_luma_samples/MinCbSizeY−pps_ref_wraparound_offset.

In previous VVC (e.g., VVC draft 8), the number of slices is signaled inthe PPS when variable single_slice_per_subpic_flag is 0, meaning thatthere is at least one subpicture containing more than one slice. In thiscase, the number of slices needs to be larger than the number ofsubpictures considering that each subpicture should contain one or morecomplete slices, which consequently results in the minimum number ofslices being 2. This is because there is at least one subpicture in onepicture.

Embodiments of the present disclosure provide methods to improve thesignaling of the slice numbers. FIG. 19 shows syntax of an examplepicture parameter set with a variable num_slices_in_pic_minus2,according to some embodiments of the present disclosure. As shown inFIG. 19, syntax elements or variables in a bitstream are shown in bold,and changes from the previous VVC (e.g., syntax shown in FIG. 11) areshown in italic type, with proposed deleted syntax being further shownin strikethrough. As shown in FIG. 19, a new variablenum_slices_in_pic_minus2 can be added to specify the value used todetermine PpsRefWraparoundOffset.

FIG. 20 shows semantics of an example improved picture parameter setwith a variable num_slices_in_pic_minus2, according to some embodimentsof the present disclosure. As shown in FIG. 20, changes from theprevious VVC (e.g., semantics shown in FIG. 12) are shown in italictype, with proposed deleted syntax being further shown in strikethrough.It is appreciated that the semantics shown in FIG. 20 can correspond tothe syntax shown in FIG. 19. In some embodiments, semantics shown inFIG. 20 corresponds to VVC (e.g., VVC draft 8).

In some embodiments, as shown in FIG. 20, the value of variablenum_slices_in_pic_minus2 plus 2 can specify the number of rectangularslices in each picture referring to the PPS. In some embodiments, asshown in FIG. 20, variable num_slices_in_pic_minus2 can replace variablenum_slices_in_pic_minus_1. In some embodiments, the value ofnum_slices_in_pic_minus2 plus 2 should be in the range of 0 toMaxSlicesPerPicture−2, inclusive, where MaxSlicesPerPicture is specifiedin VVC (e.g., VVC draft 8). When variable no_pic_partition_flag is equalto 1, the value of num_slices_in_pic_minus2 is inferred to be equal to−1.

In some embodiments, slice numbers can be signaled using a variable ofslice number minus subpicture number and then minus 1 (e.g.,num_slices_in_pic_minus_subpic_num_minus1). FIG. 21 shows syntax of anexample picture parameter set with a variablenum_slices_in_pic_minus_subpic_num_minus1, according to some embodimentsof the present disclosure. As shown in FIG. 21, syntax elements orvariables in a bitstream are shown in bold, and changes from theprevious VVC (e.g., syntax shown in FIG. 11) are shown in italic type,with proposed deleted syntax being further shown in strikethrough.

FIG. 22 shows semantics of an example improved picture parameter setwith a variable num_slices_in_pic_minus_subpic_num_minus1, according tosome embodiments of the present disclosure. As shown in FIG. 22, changesfrom the previous VVC (e.g., semantics shown in FIG. 12) are shown initalic type, with proposed deleted syntax being further shown instrikethrough. It is appreciated that the semantics shown in FIG. 22 cancorrespond to the syntax shown in FIG. 21. In some embodiments,semantics shown in FIG. 22 corresponds to VVC (e.g., VVC draft 8).

In VVC (e.g., VVC draft 8), the number of slices is signaled in PPS onlyif variable single_slice_per_subpic_flag is equal to 0 which can beequivalent to stating that there is at least one subpicture containingmore than one slice. Therefore, the number of slices should be largerthan the number of subpictures since a subpicture should contain one ormore complete slices. As a result, the minimum slice number is equal tothe number of subpictures plus 1. As shown in FIG. 21 and FIG. 22, slicenumber minus subpicture number and then minus 1 (e.g.,num_slices_in_pic_minus_subpic_num_minus1) is signaled instead of slicenumber minus 1 (e.g., num_slices_in_pic_minus1) to reduce the signaledbit number.

In some embodiments, as shown in FIG. 22, the value ofnum_slices_in_pic_minus_subpic_num_minus1 plus subpicture number andplus 1 can specify the number of rectangular slices in each picturereferring to the PPS. In some embodiments, the value ofnum_slices_in_pic_minus_subpic_num_minus1 should be in a range of 0 toMaxSlicesPerPicture minus sps_num_subpics_minus1 minus 2, inclusive,where MaxSlicesPerPicture can be specified in VVC (e.g., VVC draft 8).In some embodiments, the value ofnum_slices_in_pic_minus_subpic_num_minus1 can be inferred to be equal to(sps_num_subpics_minus1+1) when variable no_pic_partition_flag is equalto 1. In some embodiments, variable SliceNumInPic can be derived asSliceNumInPic=num_slices_in_pic_minus_subpic_num_minus1+sps_num_subpics_minus1+2.

Embodiments of the present disclosure further provide a novel way tosignal the slice address. FIG. 23 shows syntax of an example updatedslice header, according to some embodiments of the present disclosure.As shown in FIG. 23, syntax elements or variables in a bitstream areshown in bold, and changes from the previous VVC (e.g., syntax shown inFIG. 13) are shown in italic type, with proposed deleted syntax beingfurther shown in strikethrough.

In some embodiments, as shown in FIG. 23, variablepicture_header_in_slice_header_flag can be signaled in the slice headerto indicate whether the PH syntax structure is present within the sliceheader. In VVC (e.g., VVC draft 8), there is constraint on the presenceof the PH syntax structure in the slice header and the number of slicesin one picture. When the PH syntax structure is present in the sliceheader, the picture should have only one slice. Therefore, there is alsono need to signal slice address. As a result, the signaling of sliceaddress can be conditioned on picture_header_in_slice_header_flag. Asshown in FIG. 23, the value of picture_header_in_slice_header_flag canbe used as another condition to decide whether to signal variableslice_address or not. The signaling of variable slice_address is skippedwhen picture_header_in_slice_header_flag is equal to 1. In someembodiments, when variable slice_address is not signaled, it can beinferred to be 0.

Embodiments of the present disclosure further provide methods forperforming video coding. FIG. 24 shows a flowchart of an example videocoding method with a variable signaling a difference between a width ofa video frame and an offset used for computing a horizontal wrap-aroundposition, according to some embodiments of the present disclosure. Insome embodiments, method 24000 shown in FIG. 24 can be performed byapparatus 400 shown in FIG. 4. In some embodiments, method 24000 shownin FIG. 24 can be executed according to the syntax shown in FIG. 15 orsemantics shown in FIG. 16. In some embodiments, method 24000 shown inFIG. 24 includes a wrap-around motion compensation process performedaccording to the VVC standard. In some embodiments, method 24000 shownin FIG. 24 can be performed with a 360-degree video sequence as input.

In step S24010, a wrap-around motion compensation flag is received,wherein the wrap-around motion compensation flag is associated with apicture. For example, as shown in FIG. 15 or FIG. 16, the wrap-aroundmotion compensation flag can be variablepps_ref_wraparound_enabled_flag. In some embodiments, the picture is ina bitstream. In some embodiments, the picture is a part of a 360-degreevideo.

In step S24020, it is determined whether the wrap-around motioncompensation flag is enabled. For example, as shown in FIG. 15, it isdetermined if variable pps_ref_wraparound_enabled_flag is equal to 1.

In step S24030, in response to a determination that the wrap-aroundmotion compensation flag is enabled, a difference between a width of thepicture and an offset used for determining a horizontal wrap-aroundposition is received. For example, as shown in FIG. 15, when it isdetermined that variable pps_ref_wraparound_enabled_flag is equal to 1,variable pps_pic_width_minus_wraparound_offset can be received orsignaled. In some embodiments, the difference is less than or equal tothe width of the picture divided by a size of a minimum luma codingblock minus a size of luma coding tree block divided by the size of theminimum luma coding block minus 2.

In some embodiments, in S24030, receiving the difference includesreceiving a wraparound offset type flag. For example, as shown in FIG.17 and FIG. 18, a flag wraparound_offset_type can be signaled toindicate whether the signaled wraparound offset value is the originalERP picture width or the difference between the coded picture width andthe original ERP picture width. In some embodiments, as shown in FIG. 17and FIG. 18, flag wraparound_offset_type can be of values 0 or 1.

In step S24040, a motion compensation on the picture is performedaccording to the wrap-around motion compensation flag and thedifference. For example, the motion compensation on the picture can beperformed according to variables pps_ref_wraparound_enabled_flag andpps_pic_width_minus_wraparound_offset shown in FIG. 15 and FIG. 16. Insome embodiments, performing the motion compensation also includesdetermining a wraparound motion compensation offset according to thewidth of the picture and the difference and performing the motioncompensation on the picture according to the wraparound motioncompensation offset. In some embodiments, the wraparound motioncompensation offset can be determined as the width of the picturedivided by a size of a minimum luma coding block minus the difference.

FIG. 25 shows a flowchart of an example video coding method with avariable signaling a number of slices in a video frame minus 2,according to some embodiments of the present disclosure. In someembodiments, method 25000 shown in FIG. 25 can be performed by apparatus400 shown in FIG. 4. In some embodiments, method 25000 shown in FIG. 25can be executed according to the syntax shown in FIG. 19 or semanticsshown in FIG. 20. In some embodiments, method 25000 shown in FIG. 25 canbe performed according to the VVC standard.

In step S25010, a picture is received for coding. In some embodiments,the picture can comprise one or more slices. In some embodiments, thepicture is in a bitstream. In some embodiments, the one or more slicesare rectangular slices

In step S25020, a variable indicating a number of slices in the pictureminus 2 is signaled in a picture parameter set of the picture. Forexample, the variable can be num_slices_in_pic_minus2 shown in FIG. 19or FIG. 20. In some embodiments, the value of the variable plus 2 canspecify the number of rectangular slices in each picture. In someembodiments, the variable is a part of the PPS. In some embodiments,similar to the semantics shown in FIG. 20, variablenum_slices_in_pic_minus2 can replace variable num_slices_in_pic_minus_1.

FIG. 26 shows a flowchart of an example video coding method with avariable signaling a variable indicating a number of slices in the videoframe minus a number of subpictures in the video frame minus 1,according to some embodiments of the present disclosure. In someembodiments, method 26000 shown in FIG. 26 can be performed by apparatus400 shown in FIG. 4. In some embodiments, method 26000 shown in FIG. 26can be executed according to the syntax shown in FIG. 21 or semanticsshown in FIG. 22. In some embodiments, method 26000 shown in FIG. 26 canbe performed according to the VVC standard.

In step S26010, a picture is received for coding. In some embodiments,the picture can comprise one or more slices and one or more subpictures.In some embodiments, the video frame is in a bitstream. In someembodiments, the one or more slices are rectangular slices.

In step S26020, a variable indicating a number of slices in the pictureminus a number of subpictures in the picture minus 1 is signaled in apicture parameter set of the picture. For example, the variable can benum_slices_in_pic_minus_subpic_num_minus1 shown in FIG. 21 or FIG. 22.In some embodiments, a minimum slice number can be equal to the numberof subpictures plus 1. In some embodiments, as shown in FIG. 21 and FIG.22, slice number minus subpicture number and then minus 1 (e.g.,num_slices_in_pic_minus_subpic_num_minus1) can be signaled instead ofslice number minus 1 (e.g., num_slices_in_pic_minus1) to reduce thesignaled bit number. In some embodiments, the variable is a part of thePPS. In some embodiments, as shown in FIG. 22, the value ofnum_slices_in_pic_minus_subpic_num_minus1 plus subpicture number andplus 1 can specify the number of rectangular slices in each picturereferring to the PPS. In some embodiments, similar to the semanticsshown in FIG. 20, variable num_slices_in_pic_minus2 can replace variablenum_slices_in_pic_minus_1.

In some embodiments, as shown in step S26020, a variable that indicatesa number of slices in the picture can be determined according to thevariable indicating the number of slices in the video frame minus anumber of subpictures in the video frame minus 1. For example, as shownin FIG. 21 and FIG. 22, a flag or variable SliceNumInPic can be derivedaccording to variable num_slices_in_pic_minus_subpic_num_minus1.

FIG. 27 shows a flowchart of an example video coding method with avariable indicating whether a picture header syntax structure is presentwithin a slice header of a video frame, according to some embodiments ofthe present disclosure. In some embodiments, method 27000 shown in FIG.27 can be performed by apparatus 400 shown in FIG. 4. In someembodiments, method 27000 shown in FIG. 27 can be executed according tothe syntax shown in FIG. 23. In some embodiments, method 27000 shown inFIG. 27 can be performed according to the VVC standard.

In step S27010, a picture is received for coding. The picture comprisesone or more slices. In some embodiments, the picture is in a bitstream.In some embodiments, the one or more slices are rectangular slices.

In step S27020, a variable indicating whether a picture header syntaxstructure for the picture is present within a slice header for the oneor more slices is signaled. For example, the variable can bepicture_header_in_slice_header_flag shown in FIG. 23. In someembodiments, as shown in FIG. 23, when the PH syntax structure ispresent in the slice header, the picture may have only one slice.Therefore, there is also no need to signal slice address. As a result,the signaling of slice address can be conditioned on variablepicture_header_in_slice_header_flag. In some embodiments, the variableis a part of the PPS.

In some embodiments, a non-transitory computer-readable storage mediumincluding instructions is also provided, and the instructions may beexecuted by a device (such as the disclosed encoder and decoder), forperforming the above-described methods. Common forms of non-transitorymedia include, for example, a floppy disk, a flexible disk, hard disk,solid state drive, magnetic tape, or any other magnetic data storagemedium, a CD-ROM, any other optical data storage medium, any physicalmedium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROMor any other flash memory, NVRAM, a cache, a register, any other memorychip or cartridge, and networked versions of the same. The device mayinclude one or more processors (CPUs), an input/output interface, anetwork interface, and/or a memory.

It should be noted that, the relational terms herein such as “first” and“second” are used only to differentiate an entity or operation fromanother entity or operation, and do not require or imply any actualrelationship or sequence between these entities or operations. Moreover,the words “comprising,” “having,” “containing,” and “including,” andother similar forms are intended to be equivalent in meaning and be openended in that an item or items following any one of these words is notmeant to be an exhaustive listing of such item or items, or meant to belimited to only the listed item or items.

As used herein, unless specifically stated otherwise, the term “or”encompasses all possible combinations, except where infeasible. Forexample, if it is stated that a database may include A or B, then,unless specifically stated otherwise or infeasible, the database mayinclude A, or B, or A and B. As a second example, if it is stated that adatabase may include A, B, or C, then, unless specifically statedotherwise or infeasible, the database may include A, or B, or C, or Aand B, or A and C, or B and C, or A and B and C.

It is appreciated that the above described embodiments can beimplemented by hardware, or software (program codes), or a combinationof hardware and software. If implemented by software, it may be storedin the above-described computer-readable media. The software, whenexecuted by the processor can perform the disclosed methods. Thecomputing units and other functional units described in this disclosurecan be implemented by hardware, or software, or a combination ofhardware and software. One of ordinary skill in the art will alsounderstand that multiple ones of the above-described modules/units maybe combined as one module/unit, and each of the above describedmodules/units may be further divided into a plurality ofsub-modules/sub-units.

In the foregoing specification, embodiments have been described withreference to numerous specific details that can vary from implementationto implementation. Certain adaptations and modifications of thedescribed embodiments can be made. Other embodiments can be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims. It is also intended that the sequence of steps shown in figuresare only for illustrative purposes and are not intended to be limited toany particular sequence of steps. As such, those skilled in the art canappreciate that these steps can be performed in a different order whileimplementing the same method.

The embodiments may further be described using the following clauses:

1. A method for video decoding, comprising:

receiving a wrap-around motion compensation flag;

determining whether a wrap-around motion compensation is enabled basedon the wrap-around motion compensation flag;

in response to a determination that the wrap-around motion compensationis enabled, receiving data indicating a difference between a width ofthe picture and an offset used for determining a horizontal wrap-aroundposition; and performing a motion compensation according to thewrap-around motion compensation flag and the difference.

2. The method of clause 1, wherein the difference is in units of a sizeof a minimum luma coding block

3. The method of clause 2, wherein the difference is less than or equalto (pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

4. The method of clause 1, wherein performing the motion compensationfurther comprises:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

5. The method of clause 4, wherein determining the wrap-around motioncompensation offset according to the width of the picture and thedifference further comprises:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and determiningthe wrap-around motion compensation offset as being equal to the firstvalue minus the difference.

6. The method of clause 1, wherein receiving the data indicating thedifference further comprises:

receiving a wrap-around offset type flag;

determining whether the wrap-around offset type flag is equal to a firstvalue or a second value;

in response to a determination that the wrap-around offset type flag isequal to the first value, receiving the data indicating the differencebetween the width of the picture and the offset used for computing ahorizontal wrap-around position; and

in response to a determination that the wrap-around offset type flag isequal to the second value, receiving the data indicating the offset usedfor computing a horizontal wrap-around position.

7. The method of clause 6, wherein each of the first value and thesecond value is 0 or 1.

8. The method of clause 1, wherein the motion compensation is performedaccording to versatile video coding standard.

9. The method of clause 1, wherein the picture is a part of a 360-degreevideo sequence.

10. The method of clause 1, wherein the wrap-around motion compensationflag and the difference are signaled in a Picture Parameter Set (PPS).

11. A method for video decoding, comprising:

signaling a wrap-around motion compensation flag indicating whether awrap-around motion compensation is enabled;

in response to the wrap-around motion compensation flag indicating thewrap-around motion compensation is enabled, signaling data indicating adifference between a width of the picture and an offset used fordetermining a horizontal wrap-around position; and

performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

12. The method of clause 11, wherein the difference is in units of asize of a minimum luma coding block

13. The method of clause 12, wherein the difference is less than orequal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

14. The method of clause 11, wherein performing the motion compensationfurther comprises:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

15. The method of clause 14, wherein determining the wrap-around motioncompensation offset according to the width of the picture and thedifference further comprises:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and

determining the wrap-around motion compensation offset as being equal tothe first value minus the difference.

16. The method of clause 11, wherein signaling the data indicating thedifference further comprises:

signaling a wrap-around offset type flag, wherein a value of thewrap-around offset type flag can be a first value or a second value;

in response to the value of the wrap-around offset type flag is equal tothe first value, signaling the data indicating the difference betweenthe width of the picture and the offset used for computing a horizontalwrap-around position; and

in response to the value of the wrap-around offset type flag is equal tothe second value, signaling the data indicating the offset used forcomputing a horizontal wrap-around position.

17. The method of clause 16, wherein each of the first value and thesecond value is 0 or 1.

18. The method of clause 11, wherein the motion compensation isperformed according to versatile video coding standard.

19. The method of clause 11, wherein the picture is a part of a360-degree video sequence.

20. The method of clause 11, wherein the wrap-around motion compensationflag and the difference are signaled in a Picture Parameter Set (PPS).

21. A method for video coding, comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the video frame minus 2.

22. The method of clause 21, wherein the picture is in a bitstream.

23. The method of clause 21, wherein the picture is coded according toversatile video coding standard.

24. The method of clause 21, wherein the one or more slices arerectangular slices.

25. A method for video coding, comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices and one or more subpictures; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the picture minus a number ofsubpictures in the picture minus 1.

26. The method of clause 25, wherein the picture is in a bitstream.

27. The method of clause 25, further comprising:

determining a variable that indicates a number of slices in the pictureaccording to the variable indicating the number of slices in the pictureminus a number of subpictures in the picture minus 1.

28. The method of clause 25, wherein the picture is coded according toversatile video coding standard.

29. The method of clause 25, wherein the one or more slices arerectangular slices.

30. A method for video coding, comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices;

signaling a variable indicating whether a picture header syntaxstructure for the picture is present within a slice header for the oneor more slices; and

signaling a slice address according to the variable.

31. The method of clause 30, wherein the picture is in a bitstream.

32. The method of clause 30, wherein the picture is coded according toversatile video coding standard.

33. The method of clause 30, wherein the one or more slices arerectangular.

34. A system for performing video data processing, the systemcomprising:

a memory storing a set of instructions; and

a processor configured to execute the set of instructions to cause thesystem to perform:

receiving a wrap-around motion compensation flag;

determining whether a wrap-around motion compensation is enabled basedon the wrap-around motion compensation flag;

in response to a determination that the wrap-around motion compensationis enabled, receiving data indicating a difference between a width ofthe picture and an offset used for determining a horizontal wrap-aroundposition; and

performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

35. The system of clause 34, wherein the difference is in units of asize of a minimum luma coding block

36. The system of clause 35, wherein the difference is less than orequal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

37. The system of clause 34, wherein, in performing the motioncompensation, the processor is configured to execute the set ofinstructions to cause the system to perform:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

38. The system of clause 37, wherein, in determining the wrap-aroundmotion compensation offset according to the width of the picture and thedifference, the processor is configured to execute the set ofinstructions to cause the system to perform:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and

determining the wrap-around motion compensation offset as being equal tothe first value minus the difference.

39. The system of clause 34, wherein, in receiving the data indicatingthe difference, the processor is configured to execute the set ofinstructions to cause the system to perform:

receiving a wrap-around offset type flag;

determining whether the wrap-around offset type flag is equal to a firstvalue or a second value;

in response to a determination that the wrap-around offset type flag isequal to the first value, receiving the data indicating the differencebetween the width of the picture and the offset used for computing ahorizontal wrap-around position; and

in response to a determination that the wrap-around offset type flag isequal to the second value, receiving the data indicating the offset usedfor computing a horizontal wrap-around position.

40. The system of clause 39, wherein each of the first value and thesecond value is 0 or 1.

41. The system of clause 34, wherein the motion compensation isperformed according to versatile video coding standard.

42. The system of clause 34, wherein the picture is a part of a360-degree video sequence.

43. The system of clause 34, wherein the wrap-around motion compensationflag and the difference are signaled in a Picture Parameter Set (PPS).

44. A system for performing video data processing, the systemcomprising:

a memory storing a set of instructions; and

a processor configured to execute the set of instructions to cause thesystem to perform:

signaling a wrap-around motion compensation flag indicating whether awrap-around motion compensation is enabled;

in response to the wrap-around motion compensation flag indicating thewrap-around motion compensation is enabled, signaling data indicating adifference between a width of the picture and an offset used fordetermining a horizontal wrap-around position; and

performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

45. The system of clause 44, wherein the difference is in units of asize of a minimum luma coding block

46. The system of clause 45, wherein the difference is less than orequal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

47. The system of clause 44, wherein, in performing the motioncompensation, the processor is configured to execute the set ofinstructions to cause the system to perform:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

48. The system of clause 47, wherein, in determining the wrap-aroundmotion compensation offset according to the width of the picture and thedifference, the processor is configured to execute the set ofinstructions to cause the system to perform:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and

determining the wrap-around motion compensation offset as being equal tothe first value minus the difference.

49. The system of clause 44, wherein, in receiving the data indicatingthe difference, the processor is configured to execute the set ofinstructions to cause the system to perform:

signaling a wrap-around offset type flag, wherein a value of thewrap-around offset type flag can be a first value or a second value;

in response to the value of the wrap-around offset type flag is equal tothe first value, signaling the data indicating the difference betweenthe width of the picture and the offset used for computing a horizontalwrap-around position; and

in response to the value of the wrap-around offset type flag is equal tothe second value, signaling the data indicating the offset used forcomputing a horizontal wrap-around position.

50. The system of clause 49, wherein each of the first value and thesecond value is 0 or 1.

51. The system of clause 44, wherein the motion compensation isperformed according to versatile video coding standard.

52. The system of clause 44, wherein the picture is a part of a360-degree video sequence.

53. The system of clause 44, wherein the wrap-around motion compensationflag and the difference are signaled in a Picture Parameter Set (PPS).

54. A system for performing video coding, the system comprising:

a memory storing a set of instructions; and

a processor configured to execute the set of instructions to cause thesystem to perform:

receiving a picture for coding, wherein the picture comprises one ormore slices; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the video frame minus 2.

55. The system of clause 54, wherein the picture is in a bitstream.

56. The system of clause 54, wherein the picture is coded according toversatile video coding standard.

57. The system of clause 54, wherein the one or more slices arerectangular slices.

58. A system for performing video coding, the system comprising:

a memory storing a set of instructions; and

a processor configured to execute the set of instructions to cause thesystem to perform:

receiving a picture for coding, wherein the picture comprises one ormore slices and one or more subpictures; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the picture minus a number ofsubpictures in the picture minus 1.

59. The system of clause 58, wherein the picture is in a bitstream.

60. The system of clause 58, wherein the processor is configured toexecute the set of instructions to cause the system to perform:

determining a variable that indicates a number of slices in the pictureaccording to the variable indicating the number of slices in the pictureminus a number of subpictures in the picture minus 1.

61. The system of clause 58, wherein the picture is coded according toversatile video coding standard.

62. The system of clause 58, wherein the one or more slices arerectangular slices.

63. A system for performing video coding, the system comprising:

a memory storing a set of instructions; and

a processor configured to execute the set of instructions to cause thesystem to perform:

receiving a picture for coding, wherein the picture comprises one ormore slices;

signaling a variable indicating whether a picture header syntaxstructure for the picture is present within a slice header for the oneor more slices; and

signaling a slice address according to the variable.

64. The system of clause 63, wherein the picture is in a bitstream.

65. The system of clause 63, wherein the picture is coded according toversatile video coding standard.

66. The system of clause 63, wherein the one or more slices arerectangular.

67. A non-transitory computer readable medium that stores a set ofinstructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo data processing, the method comprising:

receiving a wrap-around motion compensation flag;

determining whether a wrap-around motion compensation is enabled basedon the wrap-around motion compensation flag;

in response to a determination that the wrap-around motion compensationis enabled, receiving data indicating a difference between a width ofthe picture and an offset used for determining a horizontal wrap-aroundposition; and

performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

68. The non-transitory computer readable medium of clause 67, whereinthe difference is in units of a size of a minimum luma coding block

69. The non-transitory computer readable medium of clause 68, whereinthe difference is less than or equal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

70. The non-transitory computer readable medium of clause 67, whereinperforming the motion compensation further comprises:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

71. The non-transitory computer readable medium of clause 70, whereindetermining the wrap-around motion compensation offset according to thewidth of the picture and the difference further comprises:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and

determining the wrap-around motion compensation offset as being equal tothe first value minus the difference.

72. The non-transitory computer readable medium of clause 67, whereinreceiving the data indicating difference further comprises:

receiving a wrap-around offset type flag;

determining whether the wrap-around offset type flag is equal to a firstvalue or a second value;

in response to a determination that the wrap-around offset type flag isequal to the first value, receiving the data indicating the differencebetween the width of the picture and the offset used for computing ahorizontal wrap-around position; and

in response to a determination that the wrap-around offset type flag isequal to the second value, receiving the data indicating the offset usedfor computing a horizontal wrap-around position.

73. The non-transitory computer readable medium of clause 72, whereineach of the first value and the second value is 0 or 1.

74. The non-transitory computer readable medium of clause 67, whereinthe motion compensation is performed according to versatile video codingstandard.

75. The non-transitory computer readable medium of clause 67, whereinthe picture is a part of a 360-degree video sequence.

76. The non-transitory computer readable medium of clause 67, whereinthe wrap-around motion compensation flag and the difference are signaledin a Picture Parameter Set (PPS).

77. A non-transitory computer readable medium that stores a set ofinstructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo data processing, the method comprising:

signaling a wrap-around motion compensation flag indicating whether awrap-around motion compensation is enabled;

in response to the wrap-around motion compensation flag indicating thewrap-around motion compensation is enabled, signaling data indicating adifference between a width of the picture and an offset used fordetermining a horizontal wrap-around position; and

performing a motion compensation according to the wrap-around motioncompensation flag and the difference.

78. The non-transitory computer readable medium of clause 77, whereinthe difference is in units of a size of a minimum luma coding block

79. The non-transitory computer readable medium of clause 78, whereinthe difference is less than or equal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.

80. The non-transitory computer readable medium of clause 77, whereinperforming the motion compensation further comprises:

determining a wrap-around motion compensation offset according to thewidth of the picture and the difference; and

performing the motion compensation according to the wrap-around motioncompensation offset.

81. The non-transitory computer readable medium of clause 80, whereindetermining the wrap-around motion compensation offset according to thewidth of the picture and the difference further comprises:

dividing the width of the picture in units of luma samples by a size ofa minimum luma coding block, to generate a first value; and

determining the wrap-around motion compensation offset as being equal tothe first value minus the difference.

82. The non-transitory computer readable medium of clause 77, whereinreceiving the data indicating difference further comprises:

signaling a wrap-around offset type flag, wherein a value of thewrap-around offset type flag can be a first value or a second value;

in response to the value of the wrap-around offset type flag is equal tothe first value, signaling the data indicating the difference betweenthe width of the picture and the offset used for computing a horizontalwrap-around position; and

in response to the value of the wrap-around offset type flag is equal tothe second value, signaling the data indicating the offset used forcomputing a horizontal wrap-around position.

83. The non-transitory computer readable medium of clause 82, whereineach of the first value and the second value is 0 or 1.

84. The non-transitory computer readable medium of clause 77, whereinthe motion compensation is performed according to versatile video codingstandard.

85. The non-transitory computer readable medium of clause 77, whereinthe picture is a part of a 360-degree video sequence.

86. The non-transitory computer readable medium of clause 77, whereinthe wrap-around motion compensation flag and the difference are signaledin a Picture Parameter Set (PPS).

87. A non-transitory computer readable medium that stores a set ofinstructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo coding, the method comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the video frame minus 2.

88. The non-transitory computer readable medium of clause 87, whereinthe picture is in a bitstream.

89. The non-transitory computer readable medium of clause 87, whereinthe picture is coded according to versatile video coding standard.

90. The non-transitory computer readable medium of clause 87, whereinthe one or more slices are rectangular slices.

91. A non-transitory computer readable medium that stores a set ofinstructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo coding, the method comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices and one or more subpictures; and

signaling, in a picture parameter set of the picture, a variableindicating a number of slices in the picture minus a number ofsubpictures in the picture minus 1.

92. The non-transitory computer readable medium of clause 91, whereinthe picture is in a bitstream.

93. The non-transitory computer readable medium of clause 91, furthercomprising:

determining a variable that indicates a number of slices in the pictureaccording to the variable indicating the number of slices in the pictureminus a number of subpictures in the picture minus 1.

94. The non-transitory computer readable medium of clause 91, whereinthe picture is coded according to versatile video coding standard.

95. The non-transitory computer readable medium of clause 91, whereinthe one or more slices are rectangular slices.

96. A non-transitory computer readable medium that stores a set ofinstructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo coding, the method comprising:

receiving a picture for coding, wherein the picture comprises one ormore slices;

signaling a variable indicating whether a picture header syntaxstructure for the picture is present within a slice header for the oneor more slices; and

signaling a slice address according to the variable.

97. The non-transitory computer readable medium of clause 96, whereinthe picture is in a bitstream.

98. The non-transitory computer readable medium of clause 96, whereinthe picture is coded according to versatile video coding standard.

99. The non-transitory computer readable medium of clause 96, whereinthe one or more slices are rectangular.

In the drawings and specification, there have been disclosed exemplaryembodiments. However, many variations and modifications can be made tothese embodiments. Accordingly, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is:
 1. A method for video decoding, comprising:receiving a wrap-around motion compensation flag; determining whether awrap-around motion compensation is enabled based on the wrap-aroundmotion compensation flag; in response to a determination that thewrap-around motion compensation is enabled, receiving data indicating adifference between a width of the picture and an offset used fordetermining a horizontal wrap-around position; and performing a motioncompensation according to the wrap-around motion compensation flag andthe difference.
 2. The method of claim 1, wherein the difference is inunits of a size of a minimum luma coding block
 3. The method of claim 2,wherein the difference is less than or equal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.
 4. The methodof claim 1, wherein performing the motion compensation furthercomprises: determining a wrap-around motion compensation offsetaccording to the width of the picture and the difference; and performingthe motion compensation according to the wrap-around motion compensationoffset.
 5. The method of claim 4, wherein determining the wrap-aroundmotion compensation offset according to the width of the picture and thedifference further comprises: dividing the width of the picture in unitsof luma samples by a size of a minimum luma coding block, to generate afirst value; and determining the wrap-around motion compensation offsetas being equal to the first value minus the difference.
 6. The method ofclaim 1, wherein receiving the data indicating the difference furthercomprises: receiving a wrap-around offset type flag; determining whetherthe wrap-around offset type flag is equal to a first value or a secondvalue; in response to a determination that the wrap-around offset typeflag is equal to the first value, receiving the data indicating thedifference between the width of the picture and the offset used forcomputing a horizontal wrap-around position; and in response to adetermination that the wrap-around offset type flag is equal to thesecond value, receiving the data indicating the offset used forcomputing a horizontal wrap-around position.
 7. The method of claim 6,wherein each of the first value and the second value is 0 or
 1. 8. Themethod of claim 1, wherein the motion compensation is performedaccording to versatile video coding standard.
 9. The method of claim 1,wherein the picture is a part of a 360-degree video sequence.
 10. Themethod of claim 1, wherein the wrap-around motion compensation flag andthe difference are signaled in a Picture Parameter Set (PPS).
 11. Asystem for performing video data processing, the system comprising: amemory storing a set of instructions; and one or more processorsconfigured to execute the set of instructions to cause the system toperform: receiving a wrap-around motion compensation flag; determiningwhether a wrap-around motion compensation is enabled based on thewrap-around motion compensation flag; in response to a determinationthat the wrap-around motion compensation is enabled, receiving dataindicating a difference between a width of the picture and an offsetused for determining a horizontal wrap-around position; and performing amotion compensation according to the wrap-around motion compensationflag and the difference.
 12. The system of claim 11, wherein thedifference is in units of a size of a minimum luma coding block
 13. Thesystem of claim 12, wherein the difference is less than or equal to(pps_pic_width_in_luma_samples/MinCbSizeY)−(CtbSizeY/MinCbSizeY)−2,wherein pps_pic_width_in_luma_samples is the width of the picture inunits of luma samples, MinCbSizeY is the size of the minimum luma codingblock, and CtbSizeY is a size of a luma coding tree block.
 14. Thesystem of claim 11, wherein, in performing the motion compensation, theone or more processors are configured to execute the set of instructionsto cause the system to perform: determining a wrap-around motioncompensation offset according to the width of the picture and thedifference; and performing the motion compensation according to thewrap-around motion compensation offset.
 15. The system of claim 14,wherein, in determining the wrap-around motion compensation offsetaccording to the width of the picture and the difference, the one ormore processors are configured to execute the set of instructions tocause the system to perform: dividing the width of the picture in unitsof luma samples by a size of a minimum luma coding block, to generate afirst value; and determining the wrap-around motion compensation offsetas being equal to the first value minus the difference.
 16. The systemof claim 11, wherein, in receiving the data indicating the difference,the one or more processors are configured to execute the set ofinstructions to cause the system to perform: receiving a wrap-aroundoffset type flag; determining whether the wrap-around offset type flagis equal to a first value or a second value; in response to adetermination that the wrap-around offset type flag is equal to thefirst value, receiving the data indicating the difference between thewidth of the picture and the offset used for computing a horizontalwrap-around position; and in response to a determination that thewrap-around offset type flag is equal to the second value, receiving thedata indicating the offset used for computing a horizontal wrap-aroundposition.
 17. The system of claim 16, wherein each of the first valueand the second value is 0 or
 1. 18. The system of claim 11, wherein themotion compensation is performed according to versatile video codingstandard.
 19. The system of claim 11, wherein the wrap-around motioncompensation flag and the difference are signaled in a Picture ParameterSet (PPS).
 20. A non-transitory computer readable medium that stores aset of instructions that is executable by one or more processors of anapparatus to cause the apparatus to initiate a method for performingvideo data processing, the method comprising: receiving a wrap-aroundmotion compensation flag; determining whether a wrap-around motioncompensation is enabled based on the wrap-around motion compensationflag; in response to a determination that the wrap-around motioncompensation is enabled, receiving data indicating a difference betweena width of the picture and an offset used for determining a horizontalwrap-around position; and performing a motion compensation according tothe wrap-around motion compensation flag and the difference.